Bone insert augment and offset method

ABSTRACT

A bone insert includes a cap having a convex top surface, an elongated stem, and a barrier between the cap and the stem. The stem of the bone insert is inserted into a hole formed in a host bone until the barrier is pressed against the exposed bone. The bone implant can be placed against a small focus contact point on the cap. Liquid cement can be injected into a space volume between the host bone and a bone implant. The cap can be made of a material and/or have surface features that create a strong bond with the cement when the liquid cement cures. The stem can be made of a material and/or have bone ingrowth surface features that create a strong bond with the bone.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 17/878,566, “Bone Implant Augment And OffsetMethod” filed Aug. 1, 2022, which is now U.S. Pat. No. 11,678,917, whichis a continuation-in-part of U.S. patent application Ser. No.17/069,678, “Bone Implant Augment Method And Apparatus” filed Oct. 13,2020, which is a continuation-in-part of U.S. patent application Ser.No. 15/582,380, “Bone Implant Augment Method And Apparatus” filed Apr.28, 2017 which is now U.S. Pat. No. 10,799,369 which claims priority toApplication No. 62/328,799, “Bone Implant Augment Method And Apparatus”filed Apr. 28, 2016. This application is also a continuation in part ofU.S. patent application Ser. No. 15/059,511, “Bone Implant AugmentMethod And Apparatus” filed Mar. 3, 2016, which claims priority to U.S.Provisional Patent Application No. 62/128,732, “PMMA Shims For TotalKnee Arthroplasty” filed Mar. 5, 2015, U.S. Provisional PatentApplication No. 62/133,072, “PMMA Shims For Total Knee Arthroplasty”filed Mar. 13, 2015, and U.S. Provisional Patent Application No.62/237,018, “Shims Augment System” filed Oct. 5, 2015. U.S. patentapplication Ser. No. 17/878,544, “Bone Implant Augment Method AndApparatus” filed Aug. 1, 2022 claims priority to U.S. Provisional PatentApplication No. 63/239,742, “Cement Fixation Augment And Or OffsetDevice” filed Sep. 1, 2021. U.S. patent application Ser. Nos.17/878,544, 17/069,678, 15/582,380, 15/059,511, 62/328,799, 62/237,018,63/239,742, 62/133,072, and 62/128,732 are hereby incorporated byreference in their entireties.

BACKGROUND

The proper functioning of a joint, such as the knee, hip, shoulder,ankle, or elbow can be impeded by a variety of factors, including,disease, such as osteoarthritis, mechanical injury, bone deformation,and a variety of other factors. Arthroplasty, or the surgicalrestoration of a joint, is a known procedure that is often used torelieve pain and improve joint function by replacing the diseased ordamaged articulating surfaces of a joint with prosthetic components.Achieving stable joint balance is a primary goal for arthroplastysurgeons. A balanced joint is a joint that has the proper articulationand ligamentous balance in all orientations of the joint. The patientmay be most comfortable when the artificial joint replicates thekinematics of the original, natural joint.

Various bone implant devices have been developed for orthopedic surgery.For example, a surgical implant can include an augment for the fixationof cemented total joint replacements. poly(methyl methacrylate) (PMMA)is used as the standard for cementing total joint implants to the boneof patients. More specifically, a solid metal bone augment spacer devicefor adjusting the position can be screwed to a bone implant. Liquid PMMAcan be applied to the contact areas of the bone, bone implant, and solidmetal screw device. The PMMA can then cure to secure bone implant deviceto the bone. The bone implant and solid metal screw spacer do not havebone ingrowth surfaces and do not stabilize the cement mantle.

However, PMMA cementing and bone implant failures can occur when theimplanted bone is less porous, when the bone is hard, or more sclerotic.In sclerotic bone the cement does not interdigitate or penetrate thebone in a manner in which the implant fixation is securely attached tothe bone with enough strength to resist the high repetitive forcesbetween the bone and cement mantle. What is needed are bone inserts thatcan be inserted into the bone and used to improve the bonding of thebone implant to the bone and method for attaching the bone insert andbone implant to the bone of the patient that addresses the defects withthe prior art, produces offsets at virtually any location of the bone,improves the stability of the cement and is less prone to failure.Specifically, the bone insert also interdigitates with the cement insecuring the bone insert to the cement, while the interdigitation withthe cement produces a composite construct that resists breakdown at thecement insert interface with cyclic loading and resists pullout of theinsert from the cement.

SUMMARY OF THE INVENTION

The present invention is directed towards an improved bone insert and aninstallation technique for improving the cement fixation of the boneimplant to the bone insert and host bone. A bone implant can be amedical device that is permanently attached to the bone of a patient.The bone implant can be a replacement joint such as an artificial kneewhich can be made of multiple metal components. A bone insert can be astructure that is placed into a hole formed in a bone of the patientthat provides structural support and improved bonding strength betweenthe bone implant and the bone of the patient when used with liquidcement such as PMMA. The inventive bone insert can include a cap and anelongated stem that can be highly porous structures that are coupled toeach other and separated by a barrier structure. A hole can be formed inthe host bone and the stem portion of the bone insert can be insertedinto the hole of the host bone of the patient. The barrier structure ofthe bone insert can be placed against the surfaces of the host bonesurrounding the hole and can prevent liquids from flowing into the hole.The cap of the bone insert can be a curved convex surface. For example,in some embodiments, the convex surface can be a convex spherical oraspherical surface that provides a small exposed focal point or focalspot offset contact surface area upon which the implant structure can beplaced on. The small focal point contact surface area between the boneinsert and the bone implant is important because it minimizes thecontact area between these metal components. Movement between the boneinsert and the bone implant results in friction and wear of thesecomponents at the contact areas. By minimizing the contact area, thefriction and wear of these components are also reduced and minimized.

It can be important to have a convex top surface on a bone insert havinga cap diameter that is greater than 6 mm in order to have a small focalpoint of contact. However, the convex surface of the top surface of thecap can be less important when the diameter of the cap is equal to orless than 6 mm. More specifically, a cap having a diameter less than 6mm can provide a small focal point of contact even if the upper surfaceis flat rather than convex. In other embodiments, the cap can have adiameter of between 5 mm and 60 mm or greater.

Liquid cement such as PMMA can be placed on the cap, the bondingsurface(s) of the bone implant and the resection surfaces of the hostbone. The barrier of the bone insert can prevent the liquid cement fromflowing into the elongated stem portion of the bone insert and the holeof the host bone. The liquid cement can then be cured to bond and securethe bone implant structure to the cap of the bone insert and to the hostbone. The lower surface of the barrier can have a bone ingrowth surfaceand the host bone can grow into these bone ingrowth features at thecontact areas with the barrier structure. Similarly, the stem can alsohave bone ingrowth features and the host bone can grow into thesefeatures at the inner surfaces of the hole formed in the bone.

The cap can be made of a plurality of cap micro struts that form a threedimensional lattice structure can include straight or curved struts thatcan be uniform in cross section. The cross sections of the struts can becircular, polygon, or any other geometric shape. The plurality of capmicro struts can be coupled to each other. The cap micro struts can forma plurality of tetrahedrons, three dimensional polygons, and convexpolytopes that are joined to form the cap structure. The cap microstruts three dimensional structures that are used to create the cap canbe symmetric. In some embodiments, the cap can have a hemisphericalshape. The sides of the cap can have roughly a cylindrical shape formedfrom the outer facing surfaces of the cap micro struts. The cap microstruts can be between 50-500 microns in diameter. The cap can be formedby the cap micro struts and the volume of empty space between the capmicro struts is greater than half the volume of the cap micro struts.Thus, the cap micro struts can have less than 33% of the total capvolume and the open space between the cap micro struts is greater than66% of the total cap volume. The cap micro struts can also be texturedto enhance the bonding to surgical cements such as PMMA.

In other embodiments, the cap can be made from other non-strutstructures such as a textured hollow hemispherical shell or a solid capstructure. The hollow or solid cap can have a center liquid cement inlethole and other fenestrations in the hemispherical shell for allowing theliquid cement to flow out of the cap volume. The center hole can alsomatch the size and cross section shape of an insert tool. The texturingof the hemispherical shell can enhance the bonding of the cap to thecured cement.

The elongated stem can be made of many stem micro struts with ingrowthfenestrations stem micro struts and surface texture features on theouter surfaces of the stem micro struts. The textured surfaces of thestem can provide help to secure the bone insert to the bone. In someembodiments, the stem can have a tapered stem that can be press fit intothe bone so that the outer surface of the stem creates bone ingrowthsurfaces. The bone material on the inner diameter of the hole formed inthe host bone can also grow into the ingrowth fenestrations in the stembetween the spaces between the adjacent stem micro struts to permanentlybond the bone insert into the bone of the patient. The inventive boneinserts can provide increased pullout strength (resistance to pullout)of the implant from cement with a composite multiplanar beam structure.In different embodiments, the stem can have a diameter between 2 mm and30 mm or more.

The stem micro struts are coupled to each other to form a structure thatcan have a modulus of elasticity that matches or is similar to themodulus of elasticity of the host bone. The elongated stem can have anelongated cylindrical shape formed from the outer facing surfaces of thestem micro struts. The stem micro struts can be non-linear and bentand/or curved. The stem micro struts can also be non-uniform in crosssection. The elongated stem can be a straight cylinder or a taperedcylinder that can fit into a hole drilled into a bone. The stem microstruts can form a bone implant structure that is designed to matchspecific mechanical properties of the bone that the implant is insertedinto. When a force is applied to the bone insert, the strain of the boneinsert can match the strain on the bone to minimize movement between thebone and the bone insert. The surfaces of the stem micro struts can havea textured surface or a surface roughness that can promote frictionbonding of the elongated stem to the bone and ingrowth of bone materialinto the elongated stem.

In some embodiments, the elongated stem can have a helical threadedouter surface. The elongated stem can be rotated to screw the helicalthreads into the bone. In some embodiments, the helical pedicle threadscrew can be machined into the stem portion of the bone insert.Alternatively, the helical thread can be formed in the outer facingsurfaces of the stem through the bone insert manufacturing method. Forexample, in some embodiments, the bone inserts are designed with theassistance of computer algorithms that provide the stem micro strutsthat have helical threads on the outer facing surfaces.

In other embodiments, the elongated stem can be made from othernon-strut structures. For example, the elongated stem can be a texturedporous hollow or solid structure. The hollow or solid elongated stem canhave fenestrations to allow bone ingrowth. The texturing of thehemispherical shell can enhance the physical coupling to the bone whenthe insert is initially inserted into the bone and provide bone ingrowthsurfaces to further improve bonding when the bone grows into thetextured surfaces. The fenestrations in the elongated stem can enhancethe bonding as the bone grows into the fenestrations.

The bone inserts can be fabricated with 3D printing machines such as:direct metal laser sintering (DMLS), selective laser melting (SLM),electron beam melting (EBM), laser metal deposition (LMD), selectivelaser sintering (SLS), binder jetting, metal injection molding, and anyother known 3D metal fabrication processing machines using either director indirect manufacturing techniques. The inserts can also be made usingother methods for the creation of porous metal structures. The boneinserts can be made of surgical grade metal materials such as titanium,tantalum, or any other suitable metal material. The inserts may also bemade of polymer materials that are known to ingrow with bone such aspolyetheretherketone (PEEK) and polyetherketoneketone (PEKK). In someembodiments, the PEEK or PEKK can be provided as a homogeneous filamentmaterial which can be 3D printed with a plastic compatible 3D printingmachine such as a Fused filament fabrication (FFF), fused depositionmodeling (FDM), other suitable 3D printer machines. Alternatively, thePEEK or PEKK can be provided as a homogeneous powder that can befabricated into the described bone inserts using an SLS machine or othersuitable 3D printer machines.

In some embodiments, the barrier can be a circular structure between thecap and the elongated stem. The barrier can be a solid structure thatcan prevent the liquid cement from flowing from the cap to the elongatedstem. The barrier can also provide an impact surface structure that canallow a tool to press the elongated stem of the bone insert into a boneof a patient. The bottom surface of the barrier that is placed againstthe host bone can have a textured surface that can allow bone ingrowth.In some embodiments, the barrier can have a locking mechanism that canbe secured to the end of the insertion tool. The locking mechanism canbe coupled to the insertion tool to pull and extract the bone insertfrom the bone.

For joint replacement surgeries such as total knee replacements, thereare three Morgan Jones zones of fixation. Zone 1 is the epiphysis orjoint surface, zone 2 is the metaphysis, and zone 3 is the diaphysis. Ina zone 1 region of total joint arthroplasty. The inventive bone insertdevices can not only be used to improve fixation but can also produceoffsets from bone surfaces. The inventive bone inserts can provideimproved strength characteristics for the cement interface between theimplant and the bone.

Wolff's law states that a bone in a healthy animal will adapt to theloads under which it is placed. Thus, a bone placed under high loadswill become stronger than a bone that is not exposed to high loads.Current bone implants are designed or resist fatigue and as such thebone implants can have a much higher modulus of elasticity and stiffnessthan the surrounding bone. These differences in the modulus ofelasticity and stiffness can lead to stress shielding and future boneloss. Furthermore, a mismatch in modulus between the cement and thestiffer bone implant such as the screw or rigid cage leads to increasedstresses in the cement and a breakdown of the cement over time. Theinventive bone inserts can have stems that formed from a plurality ofstem micro struts that are designed to have a modulus of elasticity thatmatches the modulus of elasticity of the host bone. By matching themodulus of elasticity, the movement and forces between the bone insertsand the host bone are minimized which can extend the life of the boneimplant.

There are various other benefits to the inventive bone inserts. The boneinsert can both secure the cement mantle to the host bone and createresistance to the breakdown of the cement at a specific location. Thethin cap micro struts can maximize the surface area interdigitation ofthe metal with the PMMA cement to create a mechanical interlock. Thethin cap micro struts can also have mechanical properties more closelymatching that of PMMA than a more solid cap construct. When the PMMAcement cures, a solid composite cap structure is created that is muchmore resistant to surface crack propagation than a pure cured PMMAcement structure. Cracks are a common mechanism of failure of PMMA intotal joint patients as a result of prolonged cyclic loads applied to abrittle cement material. The cracks result in the loosening of the boneimplant at the bone cement interface. The inventive bone insert preventsthe cracks from propagating through the cement at the composite cap ofthe bone insert which greatly improves the integrity of the boneimplant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a top view of an embodiment of a bone insert.

FIG. 2 illustrates a side view of an embodiment of a bone insert.

FIG. 3 illustrates a side view of an embodiment of a bone insert.

FIG. 4 illustrates a side view of an embodiment of a bone insert.

FIG. 5 illustrates a side view of an embodiment of a bone drill bit.

FIG. 6 illustrates a side view of a bone insert insertion tool.

FIG. 7 illustrates an end view of a bone insert insertion tool.

FIG. 8 illustrates a top view of an embodiment of a bone insert with abone insert insertion tool.

FIG. 9 illustrates a flow chart for fabricating a bone insert.

FIG. 10 illustrates a side view of a bone.

FIG. 11 illustrates a side view of a bone with resectioned surfaces.

FIG. 12 illustrates a side view of a bone with an embodiment of a boneinsert in a distal resection surface.

FIG. 13 illustrates a side view of an implant bonded to a bone and abone insert on a distal resection surface.

FIG. 14 illustrates a side of view of a bone with an embodiment of abone insert in an anterior resection surface.

FIG. 15 illustrates a side view of an implant bonded to a bone and abone insert on an anterior resection surface.

FIG. 16 illustrates an anterior view of a femur and tibia.

FIG. 17 illustrates an anterior view of a distal portion of a femur.

FIG. 18 illustrates an anterior view of a femur with a distal resectionsurface with bone insert.

FIG. 19 illustrates an anterior view of a femur with a distal resectionsurface with bone insert with a trial implant.

FIG. 20 illustrates an anterior view of a femur with a distal resectionsurface with bone inserts bonded to a final implant.

FIG. 21 illustrates an anterior view of a femur with a distal resectionsurface with a trial implant.

FIG. 22 illustrates an anterior view of a femur with a distal resectionsurface with bone inserts.

FIG. 23 illustrates an anterior view of a femur with a distal resectionsurface with bone inserts and a trial implant.

FIG. 24 illustrates an anterior view of a femur with a distal resectionsurface with bone inserts bonded to a final implant.

FIG. 25 illustrates an anterior view of a femur with a distal resectionsurface with a trial implant.

FIG. 26 illustrates an anterior view of a femur with a distal resectionsurface with a bone insert bonded to a final implant.

FIG. 27 illustrates an anterior view of a femur with a distal resectionsurface with a trial implant.

FIG. 28 illustrates an anterior view of a femur with a distal resectionsurface with a bone insert bonded to a final implant.

FIG. 29 illustrates a side view of a bone with bone inserts in anteriorand distal resection surfaces.

FIG. 30 illustrates a side view of a bone with bone inserts in anteriorand distal resection surfaces bonded to a final insert.

FIG. 31 illustrates a side view of a bone with a bone insert in aposterior resection surface.

FIG. 32 illustrates a side view of a bone with a bone insert in aposterior resection surface bonded to a final insert.

FIG. 33 illustrates a flow chart for adjusting bone inserts and bondinga final implant to a bone and the bone inserts.

FIG. 34 illustrates a flowchart of process steps for coupling an implantto a bone with bone inserts on multiple resection surfaces.

FIG. 35 illustrates a side view of a host bone and a PMMA bonereconstruction.

FIG. 36 illustrates a side view of a host bone, a bone implantreconstruction using a bone insert.

FIG. 37 illustrates a side view of liquid cement flow paths through abone insert.

FIG. 38 illustrates a side view of an embodiment of a bone insert.

FIG. 39 illustrates a top view of an embodiment of a bone insert.

FIG. 40 illustrates a side view of an embodiment of a bone insert havinga hemispherical cap.

FIG. 41 illustrates a view of a bone insert in a vertical hole in bone.

FIG. 42 illustrates a view of a bone insert in a diagonal hole in bone.

FIGS. 43A-43C illustrate side views of PMMA spacers having differentoffsets.

FIG. 44 illustrates a side view of a bone implant and PMMA spacer.

FIG. 45 illustrates a side view of a bone implant with the PMMA spacerplaced in the cap of the bone implant.

FIGS. 46A-46C illustrate side views of PMMA spacers having differentoffsets.

FIG. 47 illustrates a side view of a bone implant and PMMA spacer.

FIG. 48 illustrates a side view of a bone implant with the PMMA spacerplaced in the cap of the bone implant.

FIGS. 49-52 illustrate embodiments of offset inserts.

FIGS. 53-54 illustrate embodiments of modular bone implants.

FIGS. 55-56 illustrate embodiments of modular bone implants havingthreaded porous stems.

FIGS. 57-58 illustrate an embodiment of a modular bone implant having anexpandable threaded stem.

FIG. 59 illustrates an embodiment of a bone stem insert having anelongated cylindrical structure with tapered ends.

FIG. 60 illustrates an embodiment of a bone stem insert having anelongated cylindrical structure and a cap.

FIGS. 61 and 62 illustrate an embodiment of a bone stem insert having anon-metallic cap.

DETAILED DESCRIPTION

This invention describes a novel bone insert for ingrowth into host bonethat bridges the gap with the cement mantle connecting to the orthopedicjoint implant. The properties of the insert provide stem portions of thebone inserts with an improved modulus of elasticity matching with thehost bone and modulus of elasticity matching with the cement mantle toimprove ingrowth and reduce cement breakdown. The porosity of theinventive bone insert device allows for diffuse interdigitation of thecement with the device and the porosity of the bone facing surfaces ofthe stem promotes bone ingrowth.

FIG. 1 illustrates a top view and FIG. 2 illustrates a side view of anembodiment of a bone insert 10 having a cap 11, a stem 15, and a barrierstructure 13 between the cap 11 and the stem 15. In the illustratedexample, the cap 11 is formed from a plurality of cap micro struts 21that are coupled to each other to form a lattice structure having aplurality of cap fenestrations 23 between the cap micro struts 21. Thecap fenestrations 23 can be sized to allow liquid cement such as PMMA toeasily flow through the entire lattice of cap micro struts 21 and fillall of the cap fenestrations 23.

In the illustrated embodiment, the cap 11 can have a symmetric geometricshape formed from the cap micro struts 21 on the outer surfaces of thecap 11. The outward surfaces of the outer cap micro struts can form acylindrical or hexagonal cross section and a convex upper surface. Thecap micro struts 21 can be rigidly attached to each other and thebarrier 13 at their ends and middle portions to form a high strengtharray. The cap micro struts 21 can be straight elongated structures thathave uniform cross sections. In the illustrated embodiment, the crosssections of the cap micro struts 21 are circular. However, in otherembodiments, the cap can be any other shape and the micro struts canhave any cross section shape. The volume of the cap 11 can be defined bythe outward facing surfaces of the cap micro struts 21. The cap can beformed by the cap micro struts and the volume of empty space between thecap micro struts is greater than half the volume of the cap microstruts. The volume of the cap micro struts 21 can be 33 percent or lessof the total volume of the cap 11 with the remaining 66 percent or moreof the total volume being open cap fenestration 23 space. A higherpercentage of open cap fenestration 23 space is better for protectionpurposes. The outer surfaces of the cap micro struts 21 can have atexture or a coating that can promote adhesion to cements such as PMMA.

With reference to FIG. 1 , the cap micro struts 21 can form a centerinsertion tool recess 17 in the upper surface of the cap 11. The capmicro struts 21 may have straight and/or curved shapes. The uppersurface of the cap 11 can be comprised of curved cap micro struts 21that can form a convex hemispherical or hemi-aspherical curved uppersurface. The contact surface area is minimized to a small focal locationpoint of contact area where the upper surface of the cap 11 contacts aflat undersurface of the bone implant. While the caps 11 are illustratedas having a convex top surface in order to have a small focal point ofcontact. In other embodiments, the top surface of the cap 11 can be flator planar when the diameter of the cap 11 is less than or equal to 6 mm.The convex surface of the top surface can be less important when thediameter of the cap 11 is smaller than 6 mm because these smallerdiameter caps 11 can provide a small focal point of contact with thebone implant regardless of the cap 11 shape.

In the illustrated embodiment, the center insertion tool recess 17 canbe triangular in shape. The center insertion tool recess 17 can be freeof all cap micro struts so that the distal tip of the insert tool can beplaced between the cap micro struts 21 and pressed against the uppercenter portion of the barrier structure 13. In the illustratedembodiments, the center axis of the cap 11, barrier 13, and stem 15 ofthe bone insert 10 can all be aligned about a common center axis.

The lower ends of the cap micro struts 21 can be rigidly attached to anupper surface of the barrier structure 13 and the stem micro struts 21at the upper end of the elongated stem 15 are coupled to the bottomsurface of the barrier structure 13. The barrier structure 13 can have athin disc circular shape that can be planar, concave, or convex inshape. The barrier structure 13 can be solid or porous to gases.However, in a preferred embodiment, the barrier structure 13 shouldprevent liquids such as PMMA from flowing through the barrier structure13. The cap micro struts 21 can be radially symmetric about the centeraxis of the bone insert. Similarly, the cap fenestrations 23 between thecap micro struts 21 can be arranged symmetrically about the center axisof the bone insert 11. The cap 11 can also have cap micro struts thatare oblique supporting struts. The cap fenestrations can createsurrounding apertures of the cap 11.

The elongated stem 15 can be a cylindrical structure coupled to anopposite side of the barrier structure 13 from the cap 11. The elongatedstem 15 can be created from a plurality of stem micro struts 25 with theexterior surfaces of the stem micro struts 25 that face outward defininga roughly cylindrical or slightly tapered stem volume. In someembodiments, the stem 15 made of a bone interface mesh material whichcan be a metal mesh structure that can promote bone ingrowth and bone ongrowth. In some embodiments, a helical thread can be formed on theoutward facing stem micro struts 25 so that the bone insert 10 can bescrewed into a hole formed in a bone of a patient. The stem of the boneinserts can be made of a metal material that has surface features thatpromotes bone ingrowth and/or on growth. The stem can be made oftitanium or tantalum and the surface features of the stem can include40-800 micron depth: recesses, grooves, or other surface features suchas diameter, width and/or depth.

The volume of the elongated stem 15 can be defined by the outward facingsurfaces of the stem micro struts 25. The volume of the stem microstruts 25 can be 40 percent or less of the total volume of the elongatedstem 15 with the remaining 60 percent or more of the total volume beingopen stem fenestration 27 space. The outer surfaces of the cap microstruts 21 can have a texture or a coating that can promote adhesion tocements such as PMMA.

In contrast to the cap micro struts 21, the stem micro struts 25 can bebent and non-linear. The stem micro struts 25 can have specific designsand shapes that form a structure that can be similar or match thephysical characteristics of the bone. For example, the stem micro struts25 of the elongated stem 15 can have a modulus of elasticity thatmatches the modulus of elasticity of the bone that the bone insert 10 isinserted into. This physical characteristic matching can improve theperformance and life of the bone insert 10. When the bone insert isstressed, the bone and a bone insert 10 will deflect in strain. If thereis a mismatch between the strain of the bone and the strain of the boneinsert 10, there will be some relative stress and/or movement betweenthe bone and the bone insert 10. This stress or movement can result inweakening of the bond between the bone and the bone insert 10. However,if the modulus of elasticity of the bone insert 10 matches the modulusof elasticity of the bone the relative stress and movement is minimizedand there is much less weakening of the bond between the bone and thebone insert 10.

The mechanical properties of a typical human femoral cortical bone in alongitudinal and a transverse direction are listed below in Table 1. Thedata for the elastic modulus was obtained from the National Library ofMedicine, National Center for Biotechnology Informationhttps://www.ncbi.nlm.nih.gov/pmc/articles/PMC6053074/

TABLE 1 Longitudinal Direction Elastic Modulus 10,000-23,00 MPaTransverse Direction Elastic Modulus 3,270-12,500 MPa

Because the elastic modulus of the bone can have a wide range of values,the bone inserts 10 can be fabricated with various differentpredetermined or custom fabricated elastic modulus values. In someembodiments, the surgeon can measure or estimate the modulus ofelasticity of the bone prior to selecting the bone insert 10. A surgeoncan then select a bone insert 10 for the patient that can most closelymatch the modulus of elasticity of the bone that the bone insert 10 isinserted into. Alternatively, a custom bone insert 10 can be fabricatedfor the patient that can match the modulus of elasticity of the bonethat the bone insert 10 is inserted into.

As illustrated in Table 1, the longitudinal and transverse elasticmodulus values of a human bone can be asymmetric with different with alongitudinal elastic modulus having a higher value than the transverseelastic modulus. This is substantially different than bone insert stemsthat have uniform and/or homogeneous solid structures. In someembodiments, the elongated stems 15 of the bone inserts 10 can bedesigned using computer aided design (CAD) software and the assembly ofstrut micro struts 25 forming the stem of the bone insert 10 can beanalyzed using finite element modeling to determine the longitudinal andtransverse elastic modulus values for the elongated stems 15. Thedesigns of the strut micro struts 25 can be adjusted in the CAD systemto create longitudinal and transverse elastic modulus values that matchthe desired values that can match the measured longitudinal andtransverse elastic modulus values of the patient's bone.

It is also possible to design and fabricate bone inserts 10 havingdifferent elongated stem 15 designs. These different bone inserts 10 canbe fabricated by 3D printing and then the elongated stems 15 can beempirically measured to determine the longitudinal and transverseelastic modulus values with mechanical test equipment. The designs ofthe elongated stems 15 can then be adjusted and fabricated in iterativeprocesses until the desired longitudinal and transverse elastic modulusvalues are obtained.

In contrast to the described asymmetric elastic characteristics, anelongated stem having a uniform construction can have a longitudinalmodulus of elasticity that is the same as the transverse modulus ofelasticity. For example, an elongated stem made of a homogeneousmaterial or a composite having a uniform construction can have alongitudinal modulus of elasticity that is the same as the transversemodulus of elasticity.

FIGS. 3-4 illustrate other embodiments of the bone inserts 10. FIG. 3illustrates a side view of an embodiment of a bone insert 10 that has acap 11 that is taller and wider than the cap 11 illustrated in FIGS. 1and 2 . In this embodiment, the cap micro struts 21 extend between anupper surface of the cap 11 and a middle layer and the barrier 13. Thecap micro struts 21 intersect each other at a center portion 29 of thecap micro struts 21. The height of the cap 11 can provide a differentoffset from the surface of the bone.

FIG. 4 illustrates an embodiment of a bone insert 10 that has a tallerand narrower cap 11 and a longer elongated stem 15 than the bone insert10 illustrated in FIGS. 1 and 2 . In different embodiments, the boneinserts 10 can be made with a variety of different cap 11 heights,different elongated stem 15 lengths, and different elongated stem 15widths. The surgeon can determine the required bone offset and elongatedstem length and then select the bone insert that has a cap height andstem length that matches the required bone offset. With reference toTable 2, a group of four different bone inserts 10 that can be availablefor surgeries. In other embodiments, the different bone inserts 10 caninclude different cap 11 diameters, cap 11 heights, and stem 15 lengthsthan the dimensions of the bone inserts 10 listed in TABLE 2.

TABLE 2 Bone Insert # 1 2 3 4 Cap Diameter 7.5 mm 7.5 mm 7.5 mm 7.5 mmCap Height 3 mm 3 mm 6 mm 6 mm Stem Diameter 5 mm 5 mm 5 mm 5 mm StemHeight 10 mm 50 mm 10 mm 50 mm Taper Diameter 4-5 mm 4-5 mm 4-5 mm 4-5mm

In TABLE 2, the cap diameters are greater than the stem diameter.However, in some embodiments, the cap diameter can be equal to the stemdiameter. The barrier can have a diameter that is greater than or equalto the diameter of the cap and the elongated stem. The stems can have astraight cylindrical portion that can be 5 mm in diameter and a taperedportion that can decrease in diameter from 5 mm to 4 mm.

With reference to FIG. 5 , a side view of a drill bit 30 is illustrated.The drill bit 30 can be attached to a drill and used to form a hole in abone that is sized to closely match or be slightly smaller than theouter diameter of the stem of the bone insert. In the illustratedembodiment, the drill bit 30 has a distal end that has a bone cuttingtip 31 and a first diameter. At a proximal portion, the drill bit 30 canhave a counterbore cutting surface 33 and a stop surface 35. When thedrill bit 30 is used to drill a hole in the bone, the drill bit 30 isinserted into the bone until the stop surface 35 is used as a depthguide for the counterbore step surface of the bone. The stop surface 35functions as a visual cue for the surgeon to accurately set the depth ofthe step counterbore step surface of the bone. A hole is formed in thebone that has a cross section that matches the side view of the drillbit 30 that has a narrower and longer primary hole and a wider andshorter major hole. The length of the drill bit 30 between the end ofthe bone cutting tip 31 and the counterbore cutting surface 33 canapproximately match the length of the bone insert. Thus, a drill bit 30for a 10 mm stem height can be much shorter than a drill bit 30 for a 50mm stem

With reference to FIGS. 6 and 7 , an example of an embodiment of aninsert tool 40 is illustrated. FIG. 6 illustrates a side view and FIG. 7illustrates a front view of an insert tool 40. The insert tool 40 has adriver tip 41, a shaft 43, and a handle 45. In the illustratedembodiment, the driver tip 41 can have a triangular cross section thatcan closely fit into a triangular cross section tool recess in the capof the bone insert such as the cap shown in FIG. 1 .

With reference to FIG. 8 , the driver tip 41 can be inserted into thetool recess 17 in the cap 11 of the bone insert 10. The end of thedriver tip 41 can be pressed against the upper surface of the barrier 13of the bone insert 10. The surgeon can grasp the handle 45 of the inserttool 40 and use the insert tool 40 to press the bone insert 10 into adrilled hole in the bone until the lower surface of the barrier 13contacts the bone surface. Alternatively, the insert tool 40 can be usedto press the bone insert 10 into a surface of the bone that has not beendrilled until the lower surface of the barrier 13 contacts the outerbone surface.

A tapered stem can result in a tighter fit with the host bone as thebone insert is pressed into the bone. This tight fit produces a goodinitial fixation of the bone insert to the bone. This initial fixationis further improved as the host bone ingrows into the surface featuresand fenestrations in the stem over the months following the surgery. Thestrength of the bone can also increase over time as a function ofincreased force loading on the bone. As discussed above, Wolff's lawstates that a bone will adapt by becoming stronger if it is placed underhigher operating loads. Thus, a bone will become stronger after beingexposed to high loads over time.

In some embodiments, the insert tool 40 can have a locking mechanismthat can be used to secure the driver tip 41 to the bone insert to allowthe insert tool 40 to be used to pull the bone insert out of a bone. Forexample, by rotating the triangular driver tip 41 within the caplattice, the corners of the triangular driver tip 41 can be moved undersome of the cap micro struts 21. The upper surface of the triangulardriver tip 41 can contact the lower surfaces of the cap micro struts 21and allow the insert tool 40 to pull the bone insert 10 out of the bone.

As discussed above, in some embodiments, the outer surface of theelongated stem of the bone insert can have a helical thread. In theseembodiments, the insertion tool can be rotated in a first rotationaldirection to screw the bone insert into the hole in the bone. Theinsertion tool can also be rotated in an opposite rotational directionto unscrew the bone insert from the hole in the bone.

In the illustrated embodiments, the driver tip 41 is narrower in widththan the cap 11 of the bone insert 10. However, in other embodiments,the driver tip can surround the cap of the bone insert. As illustratedabove in FIG. 1 , the cross section of the cap 11 can be hexagonal. Insome embodiments, the driver tip can have a hexagonal head cross sectionrecess that can closely fit around the hexagonal cap. The bottom edge ofthe hexagonal head cross section recess can be placed against thebarrier to transmit an insertion force from the insert tool 40 to thebone insert.

In some embodiments, the bone insert cap and stem structures can be madeof a three-dimensional lattice construction created from many strutsthat are joined together. The cap micro struts can be coupled in alinear manner. The interdigitation of cement with the porous cap microstruts creates a composite structure that is resistant to fatiguefailure or stress crack propagation in multiple planes. The stem microstruts can be coupled in a non-linear manner. The non-linear nature orconstruction of the struts can provide improved resistance to fatiguefailure. In some embodiments, the cap and stem micro struts used to formthe bone inserts can be 25-750 microns in diameter. The use of 25-750micron diameter micro struts can improve the strength to weight ratio ofthe inserts. The 25-750 micron diameter micro struts lattice structurecan also create a bone insert device that can be readily cut with astandard operative sawblade to facilitate extraction of the cementedinsert in a revision setting.

In some embodiments, the stem micro struts can have a rough surfacefinish. The roughness of the individual struts and surfaces increasesthe surfaces area of the bone inserts to promote bone ingrowth andincreases the grip of the bone insert with the surrounding bone whenpress fit into the bone. The surface roughness can also provide for amore stable initial fixation after insertion into the bone and prior tobone ingrowth. In some embodiments, the surface roughness of the stemmicro struts can be created through 3D printers using an electron beamadditive manufacturing process.

Trabecular metals can have structural, functional, and physiologicalproperties that are similar to that of bone. Rather than being a solidmaterial, the trabecular metal can have an engineered and interconnectedinternal pore structure that can support bone fixation and boneingrowth. In some embodiments, the bone inserts can be made of poroustrabecular metal in which either the cap micro struts and/or the stemmicro struts are made of a porous trabecular metal. The cap and the stemare secured to opposite sides of a barrier. In some embodiments, aporous trabecular metal cap is secured to a porous trabecular metal stemwith a barrier design that prevents liquid cement from flowing from thecap to the stem. The barrier can be either a solid barrier or porouswith trabeculations that are too small to allow for cement flow to thestem. The porous trabecular metal bone implant can be inserted into ahole in the bone and the barrier can be pressed against the bone. LiquidPMMA cement can then be poured into the cap of the bone implant and thebarrier will prevent the liquid PMMA cement from flowing into the stemand the hole in the bone. Bone implants can be made of metal materialswith a 3D printer as described above or through other processes such aslost wax casting or other suitable fabrication processes.

With reference to FIG. 9 , a flowchart for fabricating the bone insertsis illustrated. The bone inserts can be fabricated with a direct metallaser sintering (DMLS) machine 61. The bone inserts can then be coupledto a prop support and blasted with sodium bicarbonate 63. The boneinserts can then be removed from the prop support 65. The individualbone inserts can then be abrasive media blasted 67. The bone inserts canthen be placed in a deionized (DI) water ultrasonic wash 69. The boneinserts can then be processed through hot iso-static pressing (HIP) 71.Cleaning packaging labeling (CPL) can be prepared for the bone insert73. The bone inserts can then be sterilized 75, packaged, and labeledprior to surgical use.

The inventive bone inserts can be used in primary total jointarthroplasty. This process can include drilling into a joint surfacewith a stepped drill and inserting the bone inserts into the drilledholes. The stepped drill creates a defect that matches the stem and capof the implant augment. The stepped defect is created to form a defectinto which the bone implant augment is placed in zone one. In theprimary embodiment, the depth of the defect matches the thickness of theaugment cap. In one preferred embodiment, the step drill depth isslightly deeper than the height of the cap. The step drill bit will forma hole that has a stepped hole that is slightly deeper than the cap. Thebone insert can then be pressed into the hole such that the uppersurface of the cap can be nearly flush with the surrounding cut jointbone surface adjacent to the hole. When the bone insert is placed in thehole, the cap can be lower than the outer surfaces of the bone thatsurround the hole in the bone. A small zone of PMMA cement can be placedon the upper surface of the cap. The small zone of PMMA cement will thecure forming a solid structure that will separate the top of the capfrom the lower surface of the recessed implant. The small zone of curedPMMA cement can prevent direct physical contact between the cap of thebone insert and the bone implant. The cement on the upper surface of thecap can harden so that metal micro struts on the top portion of the capare protected from direct physical contact with the metal bone implant.

Standard cementing techniques are then used in which cement is appliedto the surface of the host bone and the bone insert. The cement can flowinto the porous cap through the fenestrations between the cap microstruts. In different embodiments, the cement can flow in multipledirections through these cap fenestrations. In another embodiment, thelarger aperture on the center upper surface of the cap can facilitatethe inflow of cement. Because the center aperture is a relatively largeopening, more viscous cement types or the cement can be applied at alater time following preparation and mixing of the cement for a moreviscous cement which can flow through the fenestrations in the cap. Therequired quantity of cement can be poured into the cap or can bepressurized manually or mechanically into the cap. After the liquidcement in the cap has cured to a solid, the solid cured cement isinterdigitated with the cap to form a composite structure that isstabilized to the surrounding cement mantle and to the host bone andwill become more stable as the bone grows into the porous stem portionof the bone insert.

In other embodiments, the step drill bit can produce a deeper drilledcounterbore to produce a greater volume of cement in the cap and betweenthe cap and the implant. The hole can also be drilled in the bone inwhich the diameter of the step drill defect for the cap is larger thanthe diameter of the cap to allow for a larger mantle of cement withinthe defect surrounding the edges of the cap while the cement alsopenetrates the cap. The step drill counterbore can alternatively beshallower than the cap thickness such that when the bone insert isplaced in the drilled hole, the upper surface of the cap provides afocal location offset from the surrounding host bone surface with thecap rising above the surrounding surface of the bone.

This invention describes the novel, highly porous bone insert structurewith a high ratio of empty space and fenestrations to metal. The capportion of the bone insert can have more open empty space than the capmicro strut material by volume. This open space in the cap canfacilitate the flow of the liquid cement into the cap portion of thebone insert. As discussed above, the cap 11 can have a center insertiontool recess 17 which is larger than the other fenestrations in the cap11. The cap can have one or more insertion tool recesses that may or maynot be centered on the cap. With reference to FIG. 37 in someembodiments, the liquid cement 18 can be applied through a nozzle 17into the center insertion tool recess 17 in the cap 11 of the boneinsert 100. In some embodiments, the nozzle 17 can be placed directlyinto the center insertion tool recess 17 prior to injecting the liquidcement 18. When liquid cement 18 is injected into the cap 11, the liquidcement 18 can flow through the large open center insertion tool recess17 and then around the cap micro struts 21 into the adjacent capfenestrations 23 that are smaller than the center insertion tool recess17 between the cap micro struts 21. This flow through the capfenestrations 23 results in a thorough filling of the entire cap volumewith the PMMA cement which as discussed improves the strength of thebone implant, bone insert, and host bone assembly. The barrier 13 can bepressed against an outer surface of the bone and prevent the liquidcement 18 from flowing into the hole in the bone and into the stemportion of the bone insert 100. The lattice micro strut 21 structures ofthe cap 11 and stem can have multiple additional applications for bonefilling structures.

In another embodiment, the bone can be prepared with a stepped drill tocreate a countersunk surface in the host bone, the height of whichroughly corresponds to the height of the cap of the bone insert device.Cement is placed manually on the bone surfaces and cement is thenpressurized manually into the cap while the cement is in liquid form.The fingers of the surgeon may be large enough to seal of the edges ofthe countersunk hole and after filling the hole with liquid cement,downward pressure into the surface pressurizes the cement into theinterstice spaces of cap of the bone insert device.

This invention describes a novel bone insert having a filling latticestructure that is resistant to compression and stem surface featuresthat promote bone ingrowth. This novel lattice structure is designed tomatch the modulus of bone while also providing properties thatfacilitate cutting with standard operating room surgical bone saws.

The diameters of the core lattice strut elements can determine howresistant a metal insert structure is to being cut with a saw. Bycomposing the lattice of thin diameter elements, the resistance tocutting is greatly diminished making it much easier to cut than a solidmetal implant structure. For example, the interspersing of sub 100micron diameter cap micro struts creates areas of inherent weakness forcutting that can match the modulus of the cement thus creating astructure that is simultaneously easier to cut and resistant to cementbreakdown. Thus, the design of the bone insert can include cut areasacross the cap where the expected cuts to the insert are expected. Thesub 100 micron diameter areas can be aligned to form planar cut areas.In some embodiments, the height of the caps of the bone inserts can beshortened by cutting across the cross sections of the caps. This easilycut cap can be important in the setting of revision knee surgery whencutting across the cement mantle underneath the bone implant is oftenrequired to facilitate removal of the original bone implant prior toinstalling a revised bone implant. Cutting through the bone inserts isnot an important feature for initially securing an original bone implantto the host bone. However, the ability to easily cut through theinventive bone inserts is very important when the original bone implantneeds to removed and replaced with a replacement bone implant duringbone implant revision surgery.

There are currently no known prior art bone inserts that are used tosecure a cemented bone implant interface at a focal point on a convexcurved upper surface of a bone insert cap. The only known prior artimplant devices that are used to secure a cemented bone interface arecones that are used to secure a cement mantle in the metaphysis. Morespecifically, no bone insert augments currently exist that are optimizedto secure bone cement fixation in zone 1 of total a knee replacement.Zone 1 is at the interface below the implant along the tibial plateau.While the present invention has been described for use with kneereplacement surgery, it can also be used for other joint replacementsurgeries such as shoulder replacement surgery. Furthermore, no implantshave been described that can focally secure the cement fixation alongthe posterior flanges of the femoral components of total knees, alongthe distal femoral condylar surfaces, along the anterior femoral flangeor along the anterior surface. No known prior art implants have beendescribed that secure the cement mantle and augment the femur inanterior or posterior positions and or flanges that allows upsizing ofthe femur if over resection or bone loss has occurred in total kneearthroplasty. The combination of securing the cement mantle andaugmenting deficient bone at focal locations with minimal point contactwith bone implant has not been described in the known prior art forbroad use in multiple applications throughout joint arthroplastyincluding shoulder, elbow, finger, hip, knee and ankle arthroplasties.

There is a great need for bone inserts in joint arthroplasty withingrowth porous stems with higher porosity caps optimized for securing acement mantle. No current metal bone insert designs match the modulus ofelasticity of the insert to the modulus of elasticity of the underlyingbone as well as the modulus of elasticity of the PMMA cement. No currentbone insert designs secure the cement with a bone implant device thatmatches the modulus of the underlying PMMA cement. No current boneinsert designs match mechanical properties modulus of elasticity of boththe bone and the cement. Existing screws are too rigid and stiff at boththe stem component and at the cap relative to the bone and cement whichresults in weakening and eventual failure.

For all of these reasons, there is a need for bone filling inserts thatalso can provide a focal offset with rigid fixation prior to cementapplication that is stable in both shear and tension. Many cementedimplants fail in tension at the cement bone interface. No known priorart bone insert currently provides a focal location point of contact forthe offset of the implant and stabilization of the tensile strength ofthe bone cement interface with the bone implant.

Screws have been used to augment cement fixation and provide offset formore than three decades and have been a prior standard of care. However,current screws or Kirschner rods are not optimized for matching theelastic modulus of the host bone. Screws and specifically screw headsare also not designed for or capable of complete interdigitation withthe cement. The current shapes of the augment screws and Kirschner rodscan also create large stress risers that can result in structuralfailures. The solid or nearly solid screws are also a barrier to removalas they are not easily cut with saws which makes removal of failed ordefective bone implants very difficult.

In contrast to the prior art systems, the inventive system has manybenefits. The strength of cement used to attach the implant to the hostbone can be greatly improved when it is combined with the cap microstruts in the caps of the bone inserts. As discussed, the liquid cementcan flow into all fenestrations in the cap of the bone insert and thecement is then cured. The inventive bone insert is part of a finalcomposite structure of rigid cap micro struts oriented in multipleplanes in a lattice structure in the cured PMMA cement. Because the capstruts are thin in cross section, the cap micro struts create a largesurface area for interdigitation with the PMMA cement that creates astrong mechanical interlock. The combination of cured PMMA cement withthe cap micro struts forms a composite structure that resists crackingin multiple planes and is significantly stronger than cured PMMA cementalone. This inventive composite structure also results in much greaterbonding and physical strength between the cement and the multiplanar capmicro struts in both shear and tensile strength than a solid capstructure because the cement can bind to surface features on the capmicro struts and form a solid structure in the fenestrations between allof the cap micro struts.

The elongated stem can have an extreme surface roughness that canprovide resistance to pullout from the bone prior to bone ingrowth intothe bone implant. Extreme roughness of each beam surface can be an addedfeature. Creating the bone inserts with the desired surface roughnesscan require digital fabrication using various 3D printer technologiessuch as: direct metal laser sintering (DMLS), selective laser melting(SLM), electron beam melting (EBM), laser metal deposition (LMD),selective laser sintering (SLS), binder jetting, metal injectionmolding, and any other known 3D metal fabrication processing machines.The bone inserts can be made of surgical grade metal materials such astitanium, tantalum, or any other suitable metal material. DMLS or othermachines can fuse powdered metal media materials together to form thecap, barrier, and elongated stem of the bone insert structures. In anembodiment, the powdered metal media materials can be metals such astitanium. Other technologies such as casting, forging, and machining arenot able to create both bone implant diameters nor surface roughnessthat are desired for press fit characteristics with the surrounding boneto resist pullout and increase surface area for ingrowth. The digitalfabrication of the bone inserts can provide increased beam (strut)roughness. The roughness of the bone inserts can be increased with thetechnique of 3D printing. Multiple techniques can be used to achieve thedesired surface roughness of micro struts with minimized diameter. Insome embodiments, electron beam processing can be used to create thedesired surface roughness.

In other embodiments, the bone inserts can be made of non-metalmaterials such as polyetheretherketone (PEEK) and polyetherketoneketone(PEKK). The PEEK and PEKK can be provided as a homogeneous filamentmaterial which can be 3D printed with a plastic compatible 3D printingmachine such as a Fused filament fabrication (FFF), fused depositionmodeling (FDM), or other suitable 3D printer machines. Alternatively,the PEEK and PEKK materials can be provided in powdered form that can beused in an SLS 3D printer to fabricate the bone inserts that can includeall of the described features and material characteristics.

The process for using the inventive bone inserts can include the steps:cutting a resection surface of a host bone, drilling the cut surface ofthe host bone with a bone insert drill, placing the bone insert into thedrilled hole with the barrier pressed against an exposed surface of thehost bone, placing a liquid cement against the cut surface of the hostbone, in the cap of the bone insert, and placing the bone implantagainst the host bone and the bone insert. The barrier of the boneinsert is a solid structure that prevents the liquid cement from flowinginto the stem portion of the bone insert and the drilled hole in thehost bone. The liquid cement cures to bond the bone implant to the hostbone and the bone insert. Over time, the host bone grows into thefenestrations in the stem of the bone insert to further strengthen thebond of the bone implant to the host bone.

FIGS. 10-13 illustrates side views of a femur bone 130 to which a boneimplant 107 will be bonded to. With reference to FIG. 10 , a bone 130 isillustrated with markings 132 indicating locations of resection cuts.With reference to FIG. 11 , the bone 130 has been cut to exposeresection surfaces 131 and drilled with the bone insert drill bit. Withreference to FIG. 12 , bone inserts 100 have been placed in theresection surface 131. The bone inserts 100 includes a cap 110, abarrier 112, and a stem 101 made of a material with surface featureswhich promote bone ingrowth and/or ongrowth. The bone insert 100 hasbeen fully inserted into the bone 130 so that the barrier 112 is indirect physical contact with the resection surface 131. With referenceto FIG. 13 , the implant 107 is placed on the bone 130 with the barrier112 against the bone 130. A surface of the implant 107 is in directphysical contact with a top surface 113 of the cap 110. It can beundesirable to have directed metal to metal contact particularly if themetals that are in contact are not the same types of metal. Whendifferent metals contact each other, galvanic corrosion can occur ordirect abrasive wear. In some embodiments, the exposed outer facingsurfaces of the caps can be coated with cured PMMA that can prevent themetal bone implant from directly contacting the metal bone insert. Inother embodiments, the cap micro struts in the cap can be designed tominimize contact surface area of the cap with the implant both atcontact surface and below the contact surface of the cap. Minimizing thecontact surface area can result in much less wear at the contact areascompared to solid metal caps in which large contact areas expose theimplant to increasing wear. This invention also describes small curedPMMA spacers that can be applied to the tops of the caps to preventdirect metal on metal contact when the bone inserts are used as anoffset augment for the bone implant.

Liquid PMMA cement 109 can be applied to the exposed bone 130, the cap110 of the bone insert 100 and the implant 107. The liquid PMMA cement109 can flow into the fenestrations in the cap 110 of the bone inserts100. However, the barrier 112 of the bone insert 100 into the spacebetween the implant 107 and the bone 130. The barrier 112 can preventthe PMMA cement 109 from flowing into the stem 101 portion of the boneinsert 100. The liquid PMMA cement 109 can cure and chemically bond tothe cap 110 of the bone insert 100 and create a strong mechanical bondbetween the implant 107 and the bone 130. In an embodiment, the capmicro-struts of the cap 110 can be textured or have physical featuressuch as grooves, holes, fenestrations, etc. which can improve theinterdigitation of the liquid PMMA cement with the implant 107. Thebarrier 112 can prevent the liquid cement from flowing into the spacebetween the stem 101 and the inner diameter of the hole in the bone. Thebone can ingrow into the fenestrations in the stem 101 of the boneinsert 100 and ongrowth onto the surfaces of the stem micro-struts.

In other embodiments, the bone insert 100 can be inserted into adifferent resection surface such as an anterior resection surface. Withreference to FIG. 14 , bone inserts 100 have been placed in the anteriorresection surface 231. In this embodiment, the bone insert 100 includesa cap 110, a barrier 112, and a stem 101 made of a material with surfacefeatures which promote bone ingrowth and/or ongrowth. The bone inserts100 have been fully inserted into the bone 130 so that the barrier 112is in direct physical contact with the anterior chamfer resectionsurface 131. With reference to FIG. 15 , the implant 107 is placed onthe bone 130 with a surface of the implant 107 in direct physicalcontact with a top surface 113 of the cap 110 which is opposite thefirst surface 111. In other embodiments, the bone insert 100 can beplaced on any surface of the bone 130 between the bone 130 and theimplant 107.

The insertion of the bone insert 100 into the bone 130 can comprisevarious procedural steps. In an embodiment, the bone resection surfacecan be drilled with the bone insert drill bit and the stem 101 of thebone insert 100 can be placed into the hole formed until the barrier 112is pressed against a surface of the bone 130 to prevent liquid cementfrom flowing into the stem 101 portion of the bone insert 100. The drillcan be a stepped or counterbore drill bit which creates an insert holehaving a specific depth and diameter.

In other embodiments, the bone insert 100 can be physically pressed intothe bone 130. The force of the stem 101 against the bone 130 can createthe hole in the bone 130. The surgeon can then trial the focal offset ofthe bone insert 100 to determine the proper focal offset of the boneinsert 100. If the bone insert 100 needs to be replaced, the bone insert100 can be removed and a replacement bone insert 100 can be pressed intothe same hole formed by the previously trialed bone insert 100. The boneinserts 100 can have caps 110 that have cap micro-strut surfaces andstructural features that can allow the surgeon to easily remove the boneinsert 100 with a bone insert tool that can be used to grasp and/or pullthe cap 110 and bone insert 100 away from the bone 130. The bone insert100 can also have a barrier 112 that can be pressed against the bone 130to prevent liquid cement from flowing into the stem portion and the holedrilled in the bone 130.

The inventive process can solve a significant problem that occurs whentoo much bone is removed during resectioning. There are no preferredmethods for easily adding bone material to the cut bone surfaces otherthan using a standard screw with its aforementioned limitations.Augmenting the bone to readjust the intended position of the boneimplants on host bone to compensate for cuts in which too much bone hasbeen removed, can be very difficult without a reliable solution,especially in the setting of primary total joints in which specializedbone implants are not available. These specialized implants for revisionsurgery allow for solid metal augments to be screwed into thespecialized implants to produce thicker metal constructs in specificlocations. The assembled implants with secured augments are cementedinto host bone with the solid metal augments used to fill the bone void.Augments in these revision implants can only be secured in locations inwhich screw holes have been placed in the undersurface of the implantand typically these locations are either the distal femur or posteriorflange of the implant. These implants do not allow for focal adjustmentsat any location of the surgeon's choice and provide limited ability tomake adjustments in multiple planes. The application of the describedbone inserts solves this problem by allowing surgeons to easily adjustthe bone implant offset at any location and has the added benefit ofproviding a stronger bond between the bone and bone implant because thebone implants can be secured to bone inserts that are mechanicallybonded in holes in the bone. The caps of the bone inserts are completelyinfused with the liquid cement which strengthens and improves thestabilization of the cured cement. The caps of the bone inserts alsoprovide a small focal area of contact or no direct physical contact withthe bone implant which minimizes metal to metal contact wear. The boneinserts offer the added benefit of allowing the surgeon to place theinserts into the host bone and trial bone implants placed on the insertsto determine the correct adjustment of the component alignment. Theinserts then can be readjusted until the proper position of trialimplants is obtained. Once the proper position of the inserts isachieved, the cement can be mixed, applied to the inserts and bonesurfaces and final bone implants placed.

In contrast, a standard prior art bone implant may only rely upon PMMAcement placed on the outer surfaces of the bone to provide mechanicalbonding to the bone implant. This includes situations in which augmentsare applied to revision implants. The mechanical strength of the curedPMMA cement is much weaker than a cured PMMA cement that is reinforcedwith a metal lattice. The mechanical coupling of the cured PMMA cementto the host bone is also weaker than cured PMMA cement that is rigidlycoupled to the cap of the bone insert that has a stem that is in a holein the bone where the bone is ingrown into the stem of the bone insert.

The alignment of the implant for total knees can be variable with bothmechanical alignment and kinematic alignment being used broadly. Theneed for alignment adjustment of the implant during surgical proceduresmay be based on the discretion of the surgeon. With reference to FIG. 16, an anterior view of the knee joint is illustrated. The distal surfacesof the femur 137 can be a horizontal axis that is parallel to therotational axis of the knee 136. Each patient's anatomical geometry canbe different and the femur 139 can have various alignment configurationswith the tibia 138. In the illustrated example, the geometric axis 141of the tibia 138 can be defined by a line between the head at theproximal end of the femur 139 and the center of the knee. The geometricaxis 141 can be perpendicular to the rotational axis of the knee 136 andaligned with the center axis of the tibia 138. As illustrated, theanatomic center axis 140 of the femur 139 is angled from the geometriccenter axis 141 of the tibia 138 and is not be perpendicular to therotational axis of the knee 136 in the illustrated example. However, inother embodiments (not illustrated) the surgeon may configure thepatient's leg with the anatomical axis 140 of the femur 139 in aperpendicular orientation relative to the rotational axis 136 of theknee and aligned with the center axis 138 of the tibia 137.

FIGS. 17-20 illustrate anterior view of a femur bone 130 and boneimplant 107. With reference to FIG. 17 , the bone 130 is illustratedwith a lateral condyle of the femur (LFC) 153 and a medial condyle ofthe femur (MFC) 151. The resection cut markings 132 can extend throughportions of both the LFC 153 and the MFC 151. The resection cut markings132 may not be perpendicular to the center axis of the femur 153. FIG.18 illustrates the bone 130 after being cut with a resection surface 131and with bone inserts 100 placed in the resection surface 131 on the LFC153 and MFC 151. The bone inserts 100 have been fully inserted into thebone 130 so that barriers 112 are in direct physical contact with theresection surface 131 of the bone 130. As discussed, the barriers 112can prevent liquid PMMA from flowing into the stem portions of the boneinserts 100 and the holes in the bone 130. The implant 107 is placed onthe bone 130 and in direct physical contact with the top surfaces of thecaps 110.

With reference to FIG. 19 , the surgeon can check or test the augmentoffset of the implant 107 provided by the bone insert 100 relative tothe bone 130 and determine if the offset is correct. Checking the offsetcan include length and angular offset measurements of a trial implant108 relative to the bone 130. Checking can also be performed forfunctional performance by using trial implants 108 and the range ofmotion of the joint can be checked with the assessment of stability andmotion. For example, the offset of the bone implant 107 can be testedfor proper joint balance that has the proper articulation andligamentous balance in all orientations of the joint.

If changes need to be made, the balance of the bone implant 107 can berevised with another trial using different bone inserts 100. The boneinserts 100 that did not have the correct offset can be removed andreplaced with other bone inserts 100 that have caps 110 having differentthicknesses to change the offset length or change the angle between theresection surface 131 and the trail implant 108. The position of thetrial implant 108 and various mechanical tests can be performed todetermine if the final implant will be properly positioned by the boneinserts 100. It is also possible to fine tune the amount of offset withstep drilling to a deeper depth. If the offset is too long, then thebone inserts 100 can be removed and the step drill can be used to adjustthe depth of the step drill hole to the correct length.

With reference to FIG. 20 , once the correctly sized bone inserts 100and step drill depth are found to properly position the implant 107,liquid PMMA 109 can be applied to the caps 110 of the bone inserts 100,the resection surface 131 of the bone 130, and the bonding surface ofthe implant 107. The barriers 112 of the bone inserts 100 can preventthe liquid PMMA from flowing into the stem portions 101 of the boneinserts 100 and the hole in the bone 130. The bone 130 can ingrow intothe fenestrations in the stems 101 and ongrow onto the exposed surfacesof the stems 101. The liquid PMMA can cure to bond the implant 107 tothe bone 130 and caps 110 of the bone inserts 100. In the illustratedembodiment, the implant 107 can include a raised edge 159 which canextend around the outer perimeter of the implant 107. The raised edge159 can function to help retain the liquid PMMA cement 109 within thespace between the bone 130 and the implant 107. The height of the raisededge 159 can be less than the thickness of the caps 110 of the boneinserts 100 so that the implant 107 will contact the bone inserts 100but the raised edge 159 will not contact the bone 130. The inventivebone inserts 100 can provide bone implant 107 offsets at virtually anylocation resection surface 131 on the bone 130 and greatly improves thestability of the cured cement on the bone 130.

FIGS. 21-24 illustrate a process for adjusting the cap thicknesses ofthe inserts to properly offset the implant. With reference to FIG. 21 ,the proper predetermined length offset of the implant 107 relative tothe bone 130 can be represented by line 181. However, in the illustratedembodiment, a trial implant 108 is measured, calculated or trialed todetermine the offset of the implant. In this example, the measuredoffset line 183 is substantially shorter than the proper offset line181. The offset line 183 can be determined during a trial process of theinserts 100 where a trial implant is placed on the inserts 100 and thestability and range of motion can be tested. If these trial implant 108tests fail, the surgeon can make corrective adjustments to the caps ofthe inserts 100 to alter the offset so the final implant will match theoffset line 183. With reference to FIG. 22 , the length of the offsetbetween the bone 130 and the implant 107 has been altered by replacingthe inserts 100 with replacement inserts 185 that have thicker caps 186.With the replacement inserts 185, the offset of the final implant 107matches the proper predetermined length offset line 181. If the offsetposition of the implant needs to be shortened, the inserts 100 can bereplaced with inserts 100 having thinner caps. In this embodiment, theangle of the resection surface 131 was correct, so the thicker caps 186of the inserts 185 can have the same thickness so that the angle of theimplant 107 is not changed relative to the bone 130.

Once the proper bone inserts 100 are inserted into the bone, thebarriers of the bone inserts 100 can be pressed against the outersurface of the bone 130. Liquid PMMA 109 can be applied to the exposedareas of the bone 130, the caps 186 of the replacement inserts 185 andthe bonding surface of the final implant 107. The liquid PMMA 109 cancure to chemically bond to the caps 186 of the bone inserts 185 andmechanically bond the implant 107 to the bone 130. The barriers 112 canprevent liquid PMMA 109 from flowing into the holes in the bones 130 andthe stem portions 101 of the bone inserts 185 so that the bone 130 caningrow into the fenestrations in the stem and/or ongrow onto the contactsurfaces of the stem of the bone inserts 185.

With reference to FIG. 23 , an embodiment is illustrated where the boneinserts 100 are used with a trial implant 108. The trial implant 108 isthen measured, calculated or trialed to determine a trial offset line183. In this example, the trial offset line 183 is at a different anglethan the proper offset line 181 and an adjustment to the bone inserts100 will need to be made. The offset angle of the trial implant 108relative to the bone 130 can be changed and corrected by using boneinserts 100 having different thickness caps 110. With reference to FIG.24 , the original bone inserts 100 have been removed and replaced with afirst bone insert 187 which has a thick cap 188 in the LFC and a secondbone insert 189 which has a thicker cap 190 in the MFC. Thesereplacement bone inserts 187, 189 can cause the final implant 107 offsetto be properly angled and positioned and match the correct predeterminedoffset line 181. FIGS. 23 and 24 illustrate one embodiment of an angularcorrection. However, if the surgeon needs to angle the implant 107 moretowards the medial side, the bone insert 100 placed in the MFC 151 canhave a thinner cap 110 than the cap 110 on the insert 100 placed in theLFC 153. The use of multiple bone inserts 100 can provide greaterstability between the bone implant 107 and the bone 130.

Once the surgeon determines that the selected bone inserts 100 willprovide the proper offset of the implant 107 relative to the bone 130 bya trial process, the barriers of the bone inserts can be placed againstsurfaces of the bone 130. A liquid PMMA cement 109 can be applied to thecaps 188, 189 of the bone inserts 100, the exposed resection surface 131of the bone 130, and the bonding surfaces of the implant 107. The liquidPMMA cement 109 may also be injected and/or placed in the spaces betweenthe bone 130 and the implant 107 around the cap 110. The barrier 112 canprevent the liquid PMMA cement 109 from contacting areas between thebone 130 and the stem portions of the inserts 100. The liquid PMMAcement will harden into a solid and chemically bond to the cap microstruts of the caps 188, 190 of the bone inserts 100 and mechanicallybond the bone 130 to the implant 107. The stems 101 can have boneingrowth and ongrowth surfaces which provide interdigitation surfaceswith the bone. Once cured and fully hardened and bone has grown into thestems 101 of the inserts 100, the implant 107 will be rigidly attachedto the bone 130.

In some embodiments, it can be possible to make angular corrections tothe offset of the implant with a single implant. FIG. 25 illustrates afemur 139 with a resection surface 131. A trial implant 108 can beplaced on the resection surface 131 and the surgeon can perform a trialprocess and determine that the measured offset line 183 does not matchthe correct offset line 181 and material needs to be added to the MFC151 side of the resection surface 131. With reference to FIG. 26 , astem 101 of the bone insert 100 is inserted into the MFC 151 side of theresection surface 131 and the trial process can be repeated. In thisexample, the trial process is passed and liquid PMMA 109 can be appliedto the resection surface 131, the cap 110 of the bone insert 100 and theimplant 107 to mechanically bond the implant 107 to the femur 139.Again, the barrier 112 can prevent the liquid cement from entering thedrilled hole in the bone and the stem 101 of the bone insert 100.

With reference to FIG. 27 , a trial implant 108 is attached to theresection surface 131 and the trial process can determine that materialneeds to be added to the LFC 153 side of the resection surface. Withreference to FIG. 28 , a bone insert 100 is inserted into the LFC 153side of the resection surface 131 to correct the offset of the implant107. When the trial testing has been passed, liquid PMMA 109 can beapplied to the resection surface 131, the exposed PMMA portions of theinsert 100 and the cap 110 of the implant 107 to mechanically bond theimplant 107 to the femur 139. The barrier 112 can prevent the liquidPMMA 109 from flowing into the stem portion 101 of the bone insert 100and the hole in the femur 139

With reference to FIGS. 29-32 , side views of a bone 130 having multipleresection surfaces 131 are illustrated. In some embodiments, the boneinserts 100 can be placed on multiple resection surfaces 131 which arenot in the same plane. The bone inserts 100 can allow the surgeon tomove the implant 107 towards the anterior or posterior sides of the bone130. With reference to FIG. 29 , one or more bone inserts 100 are placedin an anterior resection surface 231 and a distal surface 131 that canbe perpendicular to a center axis of the bone 130 With reference to FIG.30 , the implant 107 position relative to the bone 130 can be adjustedtowards the anterior surface by placing tack inserts 100 in an anteriorresection surface 231. Multiple bone inserts 100 can allow for greaterstability and more complex adjustments between the bone implant 107 andthe bone 130.

With reference to FIG. 31 , one or more bone inserts 100 are placed in aposterior resection surface 233 of the bone 130 that can besubstantially parallel to a center axis of the bone 130. With referenceto FIG. 32 , the implant 107 is moved towards the posterior surfacerelative to the bone 130 by using bone inserts 100 that have differentoffsets in the posterior surfaces 233. By having bone inserts 100 inmultiple resection surfaces the surgeon can have more precise control ofthe position of the implant 107 relative to the bone 130 to match thepredetermined required offset distances, relative positions and anglesin three dimensional space. Placement of bone inserts 100 in theposterior resection surface 233 can allow the surgeon to securelyincrease the size of a femoral component to reduce a selective flexiongap imbalance.

The present invention illustrates how an implant can be offset relativeto a bone in different directions in three-dimensional space. In anembodiment, the bone can be aligned with an X, Y, and Z coordinatesystem with the center axis of the bone aligned with the Z-axis. Theanterior surface can face the X-axis and the joint at the distal end ofthe bone can rotate about the Y-axis.

FIG. 33 is an example flow chart describing the steps used to attachimplants to a resectioned bone. A bone is first resectioned 200.Trialing is then performed to determine if the implant will be properlypositioned relative to the bone or if build up from the bony surface isneeded 201. The trialing can be a test of the resection to determine ifthe position is correct. The trialing can depend upon the type of jointbeing repaired and can involve joint motion testing. The trialing willbe described in more detail later. If the resection bone is proper andno build up from the bony surface is needed, liquid PMMA can be placedon the resection bone and the implant can be placed on the liquid PMMAand the bone 202. The liquid PMMA can then cure to secure the implant inthe final position on the bone 203. If build up of the bony surface oran offset is needed, one or more bone inserts are placed into aresection surface of the bone 204. The surgeon can then determine if theone or more bone inserts will provide the proper offset 205. In someembodiments, a surgeon can use a tool such as a gauge to check theoffset of the implant relative to the bone. In other embodiments, theimplant can be placed against the inserts to determine the offset of theimplant relative to the bone. The implant placed against the insert canbe trialed for range of motion and stability to determine clinicaladequacy of the correction of the implant relative to the bone.Alternatively, any other measuring method can be used to determine theoffsets of the bone inserts. If an offset error is determined, the boneinserts can be removed from the resection surface of the bone 206 andbone inserts that provide different offsets are inserted into theresection surface of the bone 204.

In an embodiment, the surgeon can have a number of bone inserts thathave different offset sizes. For example, the different bone inserts canbe sized in 1 mm or other dimensional increments. In use, the user caninsert the stem of the bone inserts and determine that the offset is thewrong length and then find a proper length offset insert based upontrial and error. In an embodiment, a surgeon can use a kit of pairedinserts that can include various length offsets. In an embodiment, thebone inserts can be clearly marked so that the surgeon will know thedifferent offsets of the different bone insert sizes which can improvethe efficiency of the described procedures. The offsets of the boneinserts in a kit can range from 1 mm-15 mm in 1 mm increments or anyother suitable range of distances and increments. Thus, there can be 15or more bone inserts each having a different offset distance. Forexample, the bone inserts can have dot markings that indicate the offsetdistance with each dot indicating an additional 1 mm offset. In otherembodiments, the bone inserts can be numerically marked or color codedbased upon the offset distance.

If the bone inserts provide the proper implant offset relative to thebone, liquid PMMA cement can be applied to the bone inserts, bone andimplant 207. The implant is placed against the liquid PMMA which fillsall gaps between the resection surface of the bone and the implant 208.In some embodiments, the liquid PMMA can be applied with a tool such asa brush or spatula to the contact surfaces of the stem sections with theinsert and the implant. Liquid PMMA can also be injected with a toolsuch as a liquid PMMA injection gun through a nozzle into a gap betweenthe resection surface of the bone and the implant to fill this space.Thus, the liquid PMMA can be applied to the bone inserts, bone andimplant in various different ways. The liquid PMMA fills this space,cures and hardens to bond to the cured PMMA portions of the bone insertson the first and second resection surfaces. The bonding of the liquidPMMA to the cured PMMA portions of the bone inserts create a highstrength mechanical connection between the bone and the implant 209.

The use of inserts provides several benefits. The bone inserts provide ameans for correcting resection errors when excess bone material has beenremoved. The physical strength of the PMMA connection to the bone isalso improved because the stem portions of the bone inserts penetrateinto the bone and the barriers prevent the liquid PMMA from flowing intothe stem or hole in the bone. The stems and fenestrations of the boneinserts provide ongrowth and ingrowth surfaces resulting in a strongerconnection than that provided by liquid PMMA and bone interdigitationsurfaces of the bone inserts. The liquid PMMA cures around themicro-struts of the caps of the bone inserts to form a solid metallattice and PMMA cement composite structure having very high mechanicalproperties such as tensile, compression and shear strengths. Thestrength of the lattice and PMMA cement composite structure can beuniform or nearly uniform across the width and height of the curedliquid PMMA and cap portions of the bone inserts.

The inventive bone insert and method can also provide improvements forrevisions of PMMA secured bone implants that have failed. With referenceto FIG. 35 , a side view of a host bone 161 and a PMMA bonereconstruction is illustrated. In this case, a portion of the host bonehas suffered bone loss which has been cut from the bone and replacedwith PMMA 163 which has been cured to provide replacement bone material.In joint arthroplasty, liquid PMMA cement rarely penetrates more thanseveral millimeters into boney surfaces. Because the PMMA is notstrengthened it has failed and needs to be replaced with a metal boneimplant. To prepare the bone for revision surgery, the cured PMMA 163must be removed and another portion of the bone 161 is cut creating aresection surface.

FIG. 36 , a side view of a host bone 161 after revision surgery isillustrated. A bone insert 100 has been installed with the stem of thebone insert pressed into the bone 161 and the barrier of the bone insertpressed against the exposed outer surface of the bone 161. The convexouter surface of the cap of the bone insert contacts the lower surfaceof the bone implant 167 at a focal point contact area. Liquid PMMAcement has been applied to the cap portion of the bone insert and thesurface of the bone 161 adjacent to the bone implant 167. The resultingconstruct of cured PMMA cement 169 that is strengthened by the metallattice of cap micro struts and the stem that is rigidly bonded to thebone with mechanical coupling and bone ingrowth into the stem. Themechanical strength of the cured PMMA cement, the host bone, the boneinsert, and the bone implant is much better in sheer and tensilestrength than the host bone with only PMMA cement shown in FIG. 36 .

Although the bone inserts have been illustrated with caps formed fromcap micro struts, in other embodiments, the cap can be any other type ofstructure that provides an offset for the bone implant and fenestrationsthat provide liquid cement flow paths through the cap portion. Withreference to FIGS. 38 and 39 , an alternative embodiment of the boneinsert 170 is illustrated. FIG. 38 illustrates a side view and FIG. 39illustrates a top view of the bone insert 170. The elongated stem andbarrier portions of the alternative bone insert 170 are very similar tothe other illustrated bone inserts. However, the cap 171 does notinclude cap micro struts. In the illustrated embodiment, the cap 171 isa cylindrical structure that has a square cross section center orifice173 that can be used as a center tool recess. In other embodiments, thecross section can be any other geometric shape. The bone insert 170 canalso have a plurality of liquid cement flow paths 175 that can be in aradial pattern extending outward from the center orifice 173 to theouter cylindrical surface of the cap 171. The illustrated cap 171 canhave a flat top which can be appropriate when the cap 171 diameter issmaller or alternatively, the cap 171 can have a convex spherical oraspherical upper surface. As discussed above, the upper surface of thecap 171 can provide a small focal area point of contact with the boneimplant.

The elongated stem 15 of the alternative bone insert 170 can be insertedinto a drilled hole in the host bone or directly into an undrilled hostbone with an insertion tool having a corresponding cross section driverhead. The barrier 13 can be pressed against the outer surface of thehost bone to provide the desired offset of the bone implant. The boneimplant can provide a small focal point of contact with the cap 171 ofthe bone insert. Liquid cement can be poured or injected into the centerorifice 173 and can flow through the plurality of liquid cement flowpaths 175 to completely fill all fenestrations in the cap 171. The boneimplant can then be placed against the cap 171. The cement can cure tobond the bone implant to the bone insert 170 and the host bone. The boneinsert 170 can initially be held to the host bone mechanically with thefriction between the elongated stem 15 and over time host bone can growinto the surface and fenestrations in the elongated stem 15 as well asthe lower ingrowth surface of the barrier 13.

With reference to FIG. 40 , a side view of a bone insert 191 having acap 11 having a hemispherical upper surface made from a plurality of capmicro struts 21. Liquid cement can surround and flow throughfenestrations 23 between the cap micro struts 21. The cap micro struts21 at bottom of the cap 11 are coupled to an upper surface of thebarrier 13 which as discussed above prevents liquid cement from flowinginto the stem 15 portion of the bone insert 191. The stem 15 is madefrom a plurality of stem micro struts 25 with stem fenestrations 27between the adjacent stem micro struts 25. The stem micro struts 25 canhave surfaces that promote bone in growth and over time, the bone cangrow into the stem fenestrations 27. Alternatively, the stem 15 can bemade of a bone interface mesh material which can be a metal meshstructure that can promote bone ingrowth and bone on growth.

The hemispherical surface of the cap 11 can be useful to provide a smallpoint or area of contact between a bone implant and the cap 11 of thebone insert 191 which can be positioned at any angle in the bone 161. Insome embodiments, the depth and angle of the bone insert can bedetermined to avoid surgical errors. With reference to FIG. 41 , thebone insert 100 angle, depth and position are problematic because thereis insufficient bone 191 thickness at the desired bone insert 100location. If the bone insert 100 is inserted into the bone 191 at thislocation at a vertical angle, the stem 15 of the bone insert 100 willextend through the bone 191 which is unacceptable.

With reference to FIG. 42 , in order to correct this problem, the bone191 can be drilled at an angle and the bone insert 100 can be insertedat an angle so that the implanted bone insert 100 is positioned properlywithin the bone 191. The stem 15 of the bone implant 100 can have afriction fit with the inner diameter of the drilled hole and the barrier13 can be pressed against the step formed by the drill. A small contactarea on the cap 11 of the bone insert 100 can be coplanar with theresection surface of the bone 191. A planar surface of the bone implant(not shown) can then be placed onto and bonded to the resection surfaceof the bone 191 and the small contact area on the cap 11 of the boneinsert 100 with PMMA cement. The PMMA cement can fill the hole above thestep surface. However, the barrier 13 of the bone insert 100 can preventthe liquid PMMA cement from flowing into the stem 15 portion of the boneimplant 100. The PMMA cement can surround all of the stem micro strutsto form an interdigitated composite structure with the cap. The curedPMMA cement can bond the bone implant to the bone insert and theresection surface of the bone 191. Over time, the bone will grow intothe bone ingrowth surfaces on the lower surface of the barrier 13, thestem micro struts and into the fenestrations between the stem microstruts of the stem 15. Thus, the bone implant can be secured to a muchstronger structure than just PMMA cement alone.

In another embodiment, in a revision setting, after an implant hasfailed either cemented or non-cemented, frequently, a shell or rim ofbone remains once the inflammatory tissues and or cement surrounding thebone implant have been removed. In that setting, not enough bone remainsto resect bone in specific planes necessary for revision surgery. Inthis setting, the remaining rim may have complex and usually concaveconformational geometry. After drilling into the sclerotic bone and thestem of the bone insert is inserted into the drilled hole, the boneimplant is placed on the cap of the bone insert protruding into thecavity which has been left after debridement of tissues and priorremoval of the original failed implant. Cement is then placed into theirregular defect and into the cap of the bone insert to stabilize thecement filling the large defect. For total knee surgery, this situationarises in locations such as the femoral condyles or specifically theposterior femoral condyles of the tibial plateau.

FIG. 34 is a flowchart of process steps for coupling an implant to abone with bone inserts on multiple resection surfaces. In thisembodiment, the bone is resectioned forming multiple resection surfaces210. Trialing is then performed to determine if the implant will beproperly positioned relative to the bone or if build up from the bonyresection surfaces is needed 211. If the resection bone surfaces areproperly positioned and no build up from the bony surface is needed,liquid PMMA can be placed on the resection bone and the implant can beplaced on the liquid PMMA and the bone 212. The liquid PMMA can thencure to secure the implant in the final position on the bone 213. Inbuild up or an offset is needed to the resection surfaces, a first boneinsert is placed in a first resection surface of the bone 214 and asecond bone insert is placed in a second resection surface of the bone215. The surgeon can then determine if the first and second inserts willproperly position the implant offset relative to the bone 216. If theoffset is incorrect, the inserts that need to be replaced are removedfrom the bone 217 and replacement first and/or second inserts are placedinto the bone. If the inserts provide the proper implant offset relativeto the bone, liquid PMMA cement can be applied to the PMMA portions ofthe inserts, bone and implant 218. The implant is placed against theliquid PMMA which can fill all gaps between the resection surface of thebone and the implant 219. The liquid PMMA cures and hardens to bond tothe cured PMMA portions of the bone inserts on the first and secondresection surfaces. This creates a high strength PMMA structure andsecures the implant to the bone 220.

In some embodiments, the bone inserts can have offset adjustmentmechanisms for the caps. For example, during a surgery, the offsetheight of the bone insert cap may be too short. Rather than removing thebone insert, the surgeon can increase the bone insert cap offset byinserting an offset insert into the cap. FIGS. 43A, 43B, and 43Cillustrate offset inserts 14 that each have different offset heights.The offset inserts 14 can have a first portion 22 having a roundedspherical or aspherical outer surface and a second portion 24 that canhave a tapered cylindrical outer surface that are symmetric about acenter axis of the offset inserts 14. The width of the first portion 22can be wider than the width of the second portion 24 at the connectedarea to create a circular planar stop surface 25 that can beperpendicular to the center axis of the offset insert 14.

In some embodiments, the offset of a bone insert can be increased byplacing PMMA inserts into a center hole in the cap of the bone insert.that can be made of PMMA or other suitable materials. The offset inserts14 can be provided to medical service providers in sets where the offsetinserts 14 can have different vertical offset distances to provideseveral offset distance options. The offset inserts 14 can be used toincrease the height of the cap of the bone insert. As discussed above,the offset of the cap of the bone insert can contact and provide supportfor a bone implant that can be placed and secured to a bone An offsetinsert 14 having the required offset height can be selected to providethe required bone insert cap offset for the bone insert surgery. If anerror is made, the improper height offset insert 14 can be removed andreplaced with a proper height offset insert 14.

In the illustrated embodiments, the offset inserts 14 can have a firstportion 22 having a rounded spherical or aspherical surface that issymmetric about a center axis of the offset inserts 14. A lower edge ofthe first portion 22 can have an annular flat surface. The first roundedportion 22 of the PMMA insert 14 can be coupled to a tapered cylindricalsecond portion 24 of the inserts 14. The first rounded portion 22 of thePMMA offset inserts 14 can have a wider diameter than the taperedcylindrical second portion 24 of the offset inserts 14. The taperedcylindrical second portion 24 can also be symmetric about the centeraxis of the inserts 14. The PMMA inserts 14 can be fabricated by pouringliquid PMMA into molds that match the shape of the desired inserts 14.The PMMA can cure and the solid PMMA offset insert 14 can be removedfrom the molds. In other embodiments, the offset inserts 14 can befabricated by machining the insert material or any other suitablefabrication process. The PMMA offset insert 14 can a solid structure.The outer surface of the PMMA offset insert 14 can be smooth or texturedto improve the bonding of the PMMA offset insert 14 to liquid PMMAcement and the bone implant.

FIG. 44 illustrates a side view of an offset insert 14 aligned with ahole or recess 32 in the center top portion of the cap 11 of the boneinsert 12. The outer diameter of the second portion 24 of the offsetinsert 14 can be equal to or slightly smaller than an inner diameterhole or recess 32 in the cap 11 of the bone insert 12. The hole orrecess 32 can be an open space between cap micro struts 21 at the topcenter of the cap 11 of the bone insert 12. The hole or recess 32 canform a planar surface that is perpendicular to a centerline axis of thebone insert 12.

The tapered cylindrical second portion 24 of the offset inserts 14 canbe pressed into the recess 32 and the fiction between the taperedcylindrical second portion 24 of the offset inserts 14 and the innersurfaces of the recess 32 can prevent the offset insert 14 from fallingout of the bone insert 12. FIG. 45 illustrates a side view of an offsetinsert 14 fully inserted into the recess 32 in the center top portion ofthe cap 11 of the bone insert 12. A lower edge 26 of the first roundedportion 22 of the PMMA insert 14 can be pressed against the planar uppersurface of the recess 32 in the cap 11 of the bone insert 12. The loweredge 26 of the first rounded portion 22 can function as a stop when theoffset insert 14 is inserted into the bone insert 12.

During a surgery, the bone insert 12 is placed in the bone and the boneimplant can be placed against the bone insert 12. In some surgeries, thecap 11 of the bone insert 12 may not provide enough offset to supportthe bone implant to a proper position. Rather than removing andreplacing the bone insert 12 with another bone insert 12 having a longeroffset cap 11, a offset insert 14 can be placed into the cap 11 toincrease the offset of the bone insert 12. Different height offsetinserts 14 can be placed in the recess 32 until a proper offset isachieved. Once the proper height offset insert 14 is inserted, liquidcement such as PMMA can be poured over the offset insert 14 and the cap11 and a bone implant can be placed onto the bone and in contact withthe offset insert 14. The liquid cement can bond the offset insert 14 tothe cap 11 and bond the bone implant to the offset insert 14 and the cap11 of the bone insert 12. As discussed above, the barrier 13 can beplaced against the bone of the patient creating a seal that can preventthe liquid cement from flowing through the barrier 13 into the stem 15portion of the bone insert 12.

In other embodiments, the offset insert 14 can have a porous structuresuch as mesh structures that can be similar to that of the cap. FIGS.46A, 46B, and 46C illustrate porous offset inserts 14 that can be madeof high strength medical grade metal, plastic, ceramic, or othersuitable materials. Like the offset inserts 14 shown in FIGS. 43A-43C,the porous offset inserts 14 can have convex spherical or asphericalsurfaces that can provide different vertical offset distances. Forexample, the offset insert illustrated in FIG. 46A can be 3 mm, theoffset insert illustrated in FIG. 46B can be 6 mm, and the offset insertillustrated in FIG. 46C can be 9 mm. The offset inserts 14 can be usedto alter the height of the cap 11 of the bone insert 12. As discussedabove, the offset insert 14 placed in the cap of the bone insert cancontact and provide support for a bone implant. During a surgery, theoffset height of the bone insert cap can be increased by inserting anoffset insert 14 into the cap. An offset insert 14 having the requiredoffset height can be selected to provide the required bone insert capoffset for the bone insert surgery. If an error is made, the improperheight offset insert 14 can be removed and replaced with a proper heightoffset insert 14.

In the illustrated embodiments, the offset inserts 14 can have a firstportion 22 having a rounded spherical or aspherical surface that issymmetric about a center axis of the offset inserts 14. A lower edge ofthe first portion 22 can have an annular flat surface. The first roundedportion 22 of the PMMA insert 14 can be coupled to a tapered cylindricalsecond portion 24 of the inserts 14. The first rounded portion 22 of thePMMA offset inserts 14 can have a wider diameter than the taperedcylindrical second portion 24 of the offset inserts 14. The taperedcylindrical second portion 24 can also be symmetric about the centeraxis of the inserts 14. The PMMA inserts 14 can be fabricated by pouringliquid PMMA into molds that match the shape of the desired inserts 14.The PMMA can cure and the solid PMMA offset insert 14 can be removedfrom the molds. In other embodiments, the offset inserts 14 can befabricated by machining the insert material or any other suitablefabrication process. The PMMA offset insert 14 can a solid structure.The outer surface of the PMMA offset insert 14 can be smooth or texturedto improve the bonding of the PMMA offset insert 14 to liquid PMMAcement and the bone implant.

FIG. 44 illustrates a side view of an offset insert 14 aligned with ahole or recess 32 in the center top portion of the cap 11 of the boneinsert 12. The outer diameter of the second portion can be equal to orslightly smaller than an inner diameter hole in a solid cap 11 of thebone insert or a recess 32 space between cap micro struts 21 at the topcenter of the cap 11 of the bone insert 12. The tapered cylindricalsecond portion 24 of the offset inserts 14 can be pressed into therecess 32 and the fiction between the tapered cylindrical second portion24 of the offset inserts 14 and the inner surfaces of the recess 32 canprevent the offset insert 14 from falling out of the bone insert 12.FIG. 45 illustrates a side view of an offset insert 14 fully insertedinto the recess 32 in the center top portion of the cap 11 of the boneinsert 12. A lower edge of the first rounded portion 22 of the PMMAinsert 14 can be pressed against the upper edge surface of the recess 32in the cap 11 of the bone insert 12.

FIGS. 49-52 illustrate alternative embodiments for offset inserts 14that have convex first portions 22 coupled to tapered cylindrical secondportions 24. The offset inserts 14 can be inserted into the caps of boneinserts to increase the offsets of the bone inserts. The taperedcylindrical second portions 24 of the offset insert 14 can becylindrical and tapered as described above with reference to FIGS.43A-43C and 45A-45C. The tapered cylindrical second portions 24 can be ascaffold or any other structure that can have liquid cement bondingsurfaces. A second portions 24 can be scaffolds or meshes made of metalor other suitable implantable materials. When the offset inserts 14 areinserted into the bone inserts, liquid cement can be poured onto theoffset inserts 14 and the cap of the bone inserts. The taperedcylindrical second portions 24 must bond to the cured liquid cement andthe cap of the bone inserts.

FIG. 49 illustrates an offset insert 14 that can have a spherical convexfirst portions 22 that can be coupled to a tapered stem 24. Thespherical convex first portions 22 can be made of a solid structure thatcan bond to the liquid cement such as PMMA. In an embodiment, thespherical convex first portions 22 can be made of cured PMMA. In otherembodiment, the spherical convex first portions 22 can be made ofanother solid material that can have surface features that can allowfull strength bonding between a liquid cementer and the convex firstportions 22. If the offset of the bone insert needs to be increased, theoffset insert 14 can be placed into the cap and the bone implant can beplaced against the spherical convex first portions 22 of the offsetinsert 14.

FIG. 50 illustrates another embodiment of an offset insert 14 that has ahemispherical convex first portions 22 that is attached to the taperedstem 24. In this embodiment, the hemispherical convex first portions 22can be made of cured PMMA. In other embodiments, the spherical convexsurface first portion 22 can be made of another solid material that canhave surface features that can allow full strength bonding between aliquid cementer and the cap 22. The lower surface of the convex firstportions 22 can coupled to a solid circular planar structure that has alarger diameter than the tapered stem 24 forming a stop edge 26 that canbe pressed against the top edge of the cap when the offset insert 14 isinserted into the cap of the bone insert.

FIG. 51 illustrates another embodiment of an offset insert 14 that canhave a spherical convex first portion 22 that can be coupled to atapered stem 24. In this embodiment, the spherical convex first portion22 can be a hybrid structure that is made of a solid material 221 thatis bonded to a porous structure 223 that can be a scaffold. The solidmaterial 221 can surround the upper portion of the spherical convexfirst portion 22 and the center and lower portions of the sphericalconvex first portion 22 can be made of a scaffold structure. In someembodiments, the solid structure 221 can be a cured cement such as curedPMMA and the porous structure 223 can be a lattice structure made ofmetal or other suitable implantable materials.

FIG. 52 illustrates another embodiment of an offset insert 14 that canhave a hemispherical convex first portion 22 that can be coupled to atapered stem 24. In this embodiment, the hemispherical convex firstportion 22 can be a hybrid structure that is made of a solid material221 that is bonded to a porous structure 223 that can be a scaffold. Thesolid material 221 can form the upper hemispherical convex first portion22 and the inner and lower portions of the hemispherical convex firstportion 22 can be made of a scaffold structure. In the illustratedembodiment, the lower portion of the solid material 221 can create aconcave surface that can extend around the perimeter of the firstportion 22. In some embodiments, the solid structure 221 can be a curedcement such as cured PMMA and the porous structure 223 can be a latticestructure made of metal or other suitable implantable materials.

In some embodiments, the bone inserts can have a modular constructionwith caps and stems that can be separate structures that can be mixedand matched to provide surgeons with the desired combination of anoptimized stem and cap with an integrated barrier. The attachmentbetween the stem and cap/barrier can be uniform with a mechanism such asa threaded screw connection. FIGS. 53 and 54 illustrate caps 11 havingcap struts that form a convex hemispherical upper outer surface. Thestem 15 can be made of a bone interface mesh material which can be ametal mesh structure that can promote bone ingrowth and bone on growth.In other embodiments, any other stems and caps can be used with themodular system.

FIG. 53 illustrates an embodiment of a modular bone insert 50 that has amodular construction where caps 11 can be connected and disconnectedfrom the stems 15. In this example, the cap 11 and barrier 13 can have amale threaded rod 51 extending from a center portion of the barrier 13.The proximal end of the stem 15 can have a matching female threaded bore53. FIG. 53 illustrates a cross section of the female threaded bore 53portion of the stem 15. The user can rotate the cap 11 and barrier 13 tocouple the threaded rod 51 into the female threaded bore 53 until thebottom of the barrier 13 contacts the top of the stem 15. In otherembodiments, the female threaded bore can be formed in the cap 11 andbarrier 13 and a male threaded rod can be formed on the top of the stem15. In some embodiments, an adhesive can be applied to the threaded rod51 and/or the female thread bore 53 so that the cap 11 and barrier 13are permanently bonded to the stem 15 before the bone insert 12 isimplanted into the bone of the patient. If the stem 15 has externalthreads, the cap 11 can be rotated to drive the threads of the stem 15into the bone of the patient.

FIG. 54 illustrates another embodiment of a modular bone insert 50. Inthis example, the cap 11 and barrier 13 can have a protrusion 57extending from a center portion of the barrier 13. The upper portion ofthe protrusion 57 can be cylindrical and the lower portion of theprotrusion 57 can be square or rectangular in shape. The proximal end ofthe stem 15 can have a matching slot 59. The lower portion of theprotrusion 57 can be square or rectangular in shape that can closely fitinto a slot that extends to a side surface of the stem 15. The user canslide the protrusion 57 into the matching slot 59. In some embodiments,an adhesive can be applied to the protrusion 57 and/or the slot 59 sothat the cap 11 and barrier 13 are permanently bonded to the stem 15before the bone insert 12 is implanted into the bone of the patient.These configurations can allow the user to select the cap/barrier andstem and then secure the selected components together.

If the stem 15 is not threaded and the bone insert needs to be removed,the user can use a tool to grasp the cap 11 and pull the stem 15 out ofthe bone. If the stem 15 has external threads, the cap 11 can be rotatedto drive the threads of the stem 15 into the bone of the patient. Inthese illustrated embodiments, the caps 11 can be made of a lattice ofmetal struts that can form a spherical or aspherical convex outersurfaces. In other embodiments, the caps 11 can be solid structureshaving spherical or aspherical convex outer surfaces that can promotebonding with a liquid cement such as PMMA. The solid caps 11 can be madeof cured PMMA and the outer surfaces of the solid caps 11 can haveliquid cement bonding surface features such as grooves, fenestrations,holes, chemical coatings, etc. The stems 15 can be porous metalstructures that have bone ingrowth surfaces. In other embodiments, thestems 15 can be solid structures that can have bone ingrowth surfacessuch as grooves, fenestrations, holes, chemical coatings, etc.

FIGS. 55 and 56 illustrate embodiments of modular bone inserts that canhave a threaded porous stem 15. The tops of the stems 15 can have acoupling mechanism so that the stems 15 can be coupled to various cap 11designs. In the illustrated embodiments, the caps 11 can have femalethreaded bores and the stems 15 can have male threaded rods so that the

FIG. 55 illustrates a stem 15 having an externally threaded cylindricalstructure with bone ingrowth holes 57. The solid cylindrical surfaces 55of the stem 15 can have surface features such as grooves and/or surfacetreatments that can promote bone ingrowth or on growth. The threads 54on the bone inserts can be defined by the thread pitch that can bemeasured in threads per inch (TPI) such as between about 4-24 TPI ormillimeters which is the distance between two adjacent threads can bebetween about 0.3-2.5 mm. For example, the threads 54 on the stem 15. Inother embodiments, the threads 54 can have an elongated thread 54 sothat the bone insert stem 15 can be quickly screwed into a bone withfewer rotational turns. In the illustrated embodiment, there can be twoparallel threads 54 instead of a single thread 54 that extend in adouble helical path down the length of the stem 15. The top of the stem15 can have a threaded rod 51 that can be coupled to a threaded bore 53in the barrier 13 on a bottom portion of a hemispherical cap 11.

FIG. 56 illustrates an embodiment of the stem 15 having threads 54 overcylindrical structure having solid surfaces 55 and open surfaces 59. Theinterior of the stem 15 can be filled with a mesh material 56 that canfacilitate bone ingrown and ongrowth. The open side surfaces 59 can havebone ingrowth surfaces that can extend along the length of the stem 15.The bone ingrowth surfaces can be a porous metal structure that can havelarge holes or openings. The solid cylindrical surfaces 55 can also havesurface treatments that can promote bone ingrowth or on growth. The topof the stem 15 can have a threaded rod 51 that can be coupled to athreaded bore 53 in a bottom portion of a solid spherical cap 11.

In some embodiments, the bone insert can have an expanding stem 15.FIGS. 57 and 58 illustrate an embodiment of an expandable stem 15 thatcan have an internal wedge 61 that can be an elongated conical structureand a threaded screw 63. The stem 15 can be split into two or morepieces that can be separated to expand the width of the stem 15. FIG. 57illustrates the stem 15 in an unexpanded state and FIG. 58 illustratesthe stem 15 in the expanded state. In the unexpanded state, the stem 15can be inserted into a bore in a bone. In some situations, the bone canbe weak and the stem 15 can become loose in the bore hole. In order tocorrect the problem, the stem 15 can be expanded. With reference to FIG.58 , the screw 83 at the top of the stem 15 can be turned to press thewedge 81 into the stem 15 which cause the sides of the stem 15 toseparate and create a wider diameter. The top of the threaded screw 83can be screwed into a cap to provide an offset for a bone implant asdescribed above.

In some embodiments, the bone inserts can be primarily or entirely madeof an elongated cylindrical stem structure that can reinforce the cementinterface between the bone and bone implant. With reference to FIG. 59 ,an embodiment of a bone stem insert 86 can be an elongated cylindricalstructure having tapered ends. The ends of the bone insert 86 can berounded tapered points. The bone insert 86 can be divided into a boneportion 89 and a cement portion 85 that can be separated by a barrier88. The barrier 88 can be a solid non-porous structure that can occupy1-30% of the length of the bone insert 86. In the illustratedembodiment, the barrier 88 is at the center portion of the bone insert86. In other embodiments, the barrier 88 can be offset from the centerportion of the bone insert 86. A reinforcement piece 87 can be anelongated structure that can be shorter and thinner in diameter than thebone insert 86. The reinforcement piece 87 can be made of a strongmaterial such as a any of the listed metal materials. The reinforcementpiece 87 can be placed within the bone insert 86 to provide strength.The bone portion 89 can have pores and/or fenestrations and surfacefeatures that can promote bone ingrowth and on growth. The cementportion 85 can be made of a material that can bond to a liquid cementwhen it cures. Suitable materials can include a cement interface meshand/or a cured cement such as cured PMMA.

The bone stem inserts 86 can be placed into the bone with the barrier 88at or just below the outer edge of the bone surface. A bone implant canbe placed on the bone and the bone stem insert 86. Liquid cement can bepoured into the space between the bone implant and the host bone. Theliquid cement can surround the space around the bone stem insert 86 andthe bone. The barrier 88 can create a seal with the surrounding andadjacent outer bone surface and prevent the liquid cement from flowinginto the porous bone portion 89 or into the bone. The liquid cement cancure to secure the cement portion 85 of the bone stem inserts 86 to thebone and bone implant. The bone can grow into and onto the porous boneportion 89 of the bone stem inserts 86. The bone stem insert 86 canfunction as a reinforcement for the cement between the bone and the boneimplant.

FIG. 60 illustrates another embodiment of a bone stem insert 96 havingan elongated cylindrical structure that can have a bone portion 99 and acement portion 95 that are separated by a transition barrier portion 98.The barrier 98 can be a solid non-porous structure that can occupy 1-30%of the length of the bone insert 96. In the illustrated embodiment, thebarrier 98 is at the center portion of the bone insert 96. In otherembodiments, the barrier 98 can be offset from the center portion of thebone insert 96.

In this example, a cap 11 is coupled to an end of the cement portion 85.However, the cap 11 is optional and the bone stem insert 96 can be usedwithout the cap 11. The illustrated bone portion 99 can be made of abony mesh that has surfaces, pores, and fenestrations that can promotebone on growth and bone ingrowth so that the bone stem insert 96 canbecome more securely bonded to the bone over time. The cement portion 95can be made of a cement mesh that can have pores, fenestrations, andcement flow paths that can allow liquid cement to easily flow throughand saturate the cement portion 95.

The bone stem inserts 96 can be placed into the bone with the barrier 98at the outer edge surface of the bone. A bone implant can be placed onthe bone and the bone stem insert 96. Liquid cement can be poured intothe space between the bone implant can be placed on the bone. The liquidcement can surround the space around the bone stem insert 96 and thebone. The barrier 98 can create a seal with the surrounding bone andprevent the liquid cement from flowing into the porous bone portion 99or into the bone. The liquid cement can cure to secure the cementportion 95 of the bone stem inserts 96 to the bone and bone implant. Thebone can grow into and onto the porous bone portion 99 of the bone steminserts 96. The bone stem insert 96 can function as a reinforcement forthe cement between the bone and the bone implant.

The bone inserts described above can be made of surgical grade metalmaterials such as titanium, tantalum, or any other suitable metalmaterial and/or the bone inserts may also be made of polymer materialsthat are known to ingrow with bone such as polyetheretherketone (PEEK)and polyetherketoneketone (PEKK).

The bone inserts and offset inserts can be configured to prevent metalto metal contact. Specifically, the contact between the metal boneimplant and the bone inserts and offset inserts should not be a metal tometal contact. If the bone inserts or offset inserts are made of a metalmaterial, these metal structures can be coated with a non-metal coatingthat can provide a strong bond with liquid cement such as PMMA. In someembodiments, the metal bone inserts and/or metal offset inserts canoffset can be pre-coated with a layer of PMMA. Alternatively, a user cancoat the metal bone inserts and metal offset inserts with PMMA.

The described bone inserts and offset inserts can be packaged in kitsthat include multiple bone inserts and offset inserts that can havedifferent sizes and offsets as described above. These kits may also beprovided with a tray that liquid PMMA cement can poured in. The boneinserts and offset inserts can be placed into the liquid PMMA cement fora couple of minutes so that the liquid PMMA surrounds and coats some orall surfaces of the bone inserts and offset inserts. The PMMA coatedbone inserts and offset inserts can then be removed and the PMMA cementcan cure on the bone inserts and offset inserts. The PMMA coated boneinserts and offset inserts can then be placed in the bone of the patientand in contact with a metal bone implant and the PMMA coating willprevent direct metal to metal contact.

With reference to FIGS. 61 and 62 , another method and apparatus forpreventing metal to metal contact can be to place covers 91 made ofnon-metal materials over the outer surfaces of the bone insert cap 11and/or offset insert 22. FIG. 61 illustrates an offset insert 22 thathas been attached to the cap 11 of a bone insert 12 and a cover 91 thatis porous and made of cured PMMA. The cover 91 can be placed onto theoffset insert 22 as illustrated in FIG. 62 .

In the illustrated example, the cover 91 can have a hemispherical shapethat can have an inner concave surface that matches the convex outersurface of the offset insert 22. In other embodiments, the cover 91 canhave an inner concave surface that matches the convex outer surface ofboth the offset insert 22 and the bone insert cap 11. The cover 91 canhave a thin uniform thickness that can match the outer surfaces of thebone insert cap 11 and/or offset insert 22. The cover 91 can have athickness of about 0.1 to 1.0 mm. The cover 91 can have a porous surfaceand/or fenestrations that can allow liquid cement such as PMMA to passthrough the cover 91 while preventing metal to metal contact between thebone insert cap 11 and/or offset insert 22 and a metal bone implant. Theedge of the cover 91 can have an inward facing lip or other clipfeatures that can cause the cover 91 to snap into place and maintainattachment to the insert cap 11 and/or the offset insert 22.

The present disclosure, in various embodiments, includes components, andapparatus substantially as depicted and described herein, includingvarious embodiments, sub-combinations, and subsets thereof. Those ofskill in the art will understand how to make and use the presentdisclosure after understanding the present disclosure. The presentdisclosure, in various embodiments, includes providing devices andprocesses in the absence of items not depicted and/or described hereinor in various embodiments hereof, including in the absence of such itemsas may have been used in previous devices or processes, e.g., forimproving performance, achieving ease and/or reducing cost ofimplementation. Rather, as the flowing claims reflect, inventive aspectslie in less than all features of any single foregoing disclosedembodiment.

What is claimed is:
 1. A method for coupling a bone insert to a bonecomprising: providing the bone insert having a cap havinginterdigitation surfaces, an elongated stem having bone ongrowth surfacefeatures on an outer surface of the elongated stem that extends downwardfrom the barrier structure, and a barrier structure coupled between alower portion of the cap and an upper portion of the elongated stem;inserting the stem of the bone insert into the bone; placing the barrierstructure against a surface of the bone; pouring liquid poly(methylmethacrylate) cement into at least one of the plurality of fenestrationsin the cap; transmitting the liquid poly(methyl methacrylate) cementonto the interdigitation surfaces on the cap; and blocking the liquidpoly(methyl methacrylate) cement from flowing through the cap throughthe barrier structure to the elongated stem.
 2. The method of claim 1further comprising: drilling a hole in the bone surface before the stemis inserted into the hole in the bone surface.
 3. The method of claim 1further comprising: drilling the bone with a stepped drill bit; whereinthe stem is inserted into the hole in the bone surface and the barrieris placed against a step in the hole formed by the stepped drill bit. 4.The method of claim 1 further comprising: providing a polymer coating ona portion of an upper and outer surface of the cap; placing a boneimplant against the polymer coating on the cap at a focal point contactarea that is less than 60 square millimeters; placing poly(methylmethacrylate) cement on the focal point contact area; and curing thepoly(methyl methacrylate) cement to bond the bone implant to the cap. 5.The method of claim 1 further comprising: providing a cured layer ofliquid poly(methyl methacrylate) cement on the cap of the bone insert;placing a bone implant against the cured layer of liquid poly(methylmethacrylate) cement on the cap at a focal point contact area that isless than 60 square millimeters; and curing the poly(methylmethacrylate) cement to bond the bone implant to the cap and the bone.6. The method of claim 1 further comprising: providing bone ongrowthsurfaces a lower portion of the barrier structure; and receiving bonematerial onto the bone ongrowth surfaces on the lower portion of thebarrier structure.
 7. The method of claim 1 further comprising: forminghelical threads on external surfaces of the stem of the bone insert;rotating the bone insert relative to the bone to screw the bone insertinto the bone.
 8. A method for coupling a bone insert to a bonecomprising: providing the bone insert having a cap havinginterdigitation surfaces, a polymer coating on a portion of an upper andouter surface of the cap, an elongated stem having bone ongrowth surfacefeatures on an outer surface of the elongated stem that extends downwardfrom the barrier structure, and a barrier structure coupled between alower portion of the cap and an upper portion of the elongated stem;inserting the stem of the bone insert into the bone; placing the barrierstructure against a surface of the bone; pouring liquid poly(methylmethacrylate) cement onto the interdigitation surfaces on the cap;transmitting the liquid poly(methyl methacrylate) cement through theplurality of fenestrations in the cap to an outer surface of the cap;and blocking the liquid poly(methyl methacrylate) cement from flowinginto the elongated stem of the bone insert by the barrier structure. 9.The method of claim 8 further comprising: drilling a hole in the bonesurface before the stem is inserted into the hole in the bone surface.10. The method of claim 8 further comprising: drilling the bone with astepped drill bit; wherein the stem is inserted into the hole in thebone surface and the barrier is placed against a step in the hole formedby the stepped drill bit.
 11. The method of claim 8 further comprising:placing a bone implant against the cap of the bone insert at a focalpoint contact area that is less than 30 square millimeters; and curingthe poly(methyl methacrylate) cement to bond the bone implant to thecap.
 12. The method of claim 8 further comprising: providing a polymercoating on a portion of an upper and outer surface of the cap; placing abone implant against the polymer coating on the cap at a focal pointcontact area that is less than 30 square millimeters; placingpoly(methyl methacrylate) cement on the focal point contact area of thecap; and curing the poly(methyl methacrylate) cement to bond the boneimplant to the cap.
 13. The method of claim 8 further comprising:providing a cured layer of liquid poly(methyl methacrylate) cement onthe cap of the bone insert; placing a bone implant against the curedlayer of liquid poly(methyl methacrylate) cement on the cap at a focalpoint contact area that is less than 30 square millimeters; and curingthe poly(methyl methacrylate) cement to bond the bone implant to the capand the bone.
 14. The method of claim 8 further comprising: providingbone ongrowth surfaces a lower portion of the barrier structure and theplurality of stem micro struts; and receiving bone material into thebone ingrowth surfaces on the lower portion of the barrier structure andthe plurality of stem micro struts.
 15. The method of claim 8 furthercomprising: forming helical threads on external surfaces of the stem ofthe bone insert; rotating the bone insert relative to the bone to screwthe bone insert into the bone.
 16. A method for coupling a bone insertto a bone comprising: providing the bone insert having a cap having atool recess, the cap having interdigitation surfaces, a barrierstructure coupled to a lower portion of the cap and an elongated stemhaving bone ongrowth surface features, the elongated stem extendsdownward from the barrier structure; providing an insert tool having ahandle coupled to the proximal portion of the insert tool, a shaftcoupled to the handle, and a driver on a distal end of the shaft;inserting the driver of the insert tool into the tool recess in the capof the bone insert; inserting the stem of the bone insert into the boneusing the insert tool; placing the barrier structure against the bone;removing the driver of the insert tool from the recess in the cap of thebone insert; pouring liquid poly(methyl methacrylate) cement onto theinterdigitation surfaces on the cap; and blocking the liquid poly(methylmethacrylate) cement from flowing through the barrier structure into theelongated stem of the bone insert.
 17. The method of claim 16 furthercomprising: drilling the bone with a stepped drill bit; wherein the stemis inserted into the hole in the bone surface and the barrier is placedagainst a step in the hole formed by the stepped drill bit.
 18. Themethod of claim 16 further comprising: locking the driver to the recessin the cap of the bone insert; and extracting the bone insert from thebone using the insert tool.
 19. The method of claim 16 furthercomprising: forming helical threads on external surfaces of the stem ofthe bone insert; wherein the inserting of the stem of the bone insertinto the bone surface includes rotating the bone insert in a firstrotational direction to screw the bone insert into the bone using theinsert tool.
 20. The method of claim 16 further comprising: placing abone implant against the cap at a focal point contact area that is lessthan 30 square millimeters; and curing the poly(methyl methacrylate)cement to bond the bone implant to the cap and the bone.